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Discussion Starter #1
I am a new member to the forum, but I have spent the past month reading every thread the search engine on the forum would offer in regards to my problem.

First some background. About 2 months ago I purchased a used 07 Canyon Z71 Crew Cab. The truck had been totaled in an accident (I believe it was tipped on its side) but has been restored. I know the guy who owned it, and it had driven it for 2 years after the repairs without a single problem. The truck has approx 60K miles, a 2 inch lift and had 265-75/R16 Cooper ATP’s on it, and had corvette servos installed at a transmission shop, otherwise it is stock. I have the 3.73 rear end. The day I bought the truck I had to replace the fuel pump and the battery in the same day.

The truck starts and runs great, however I only get about 13 miles a gallon mixed city and highway. As I mentioned I have read every post the 355 nation search engine would give me, so let me answer some of the usual questions right away. And yes, I actually calculate with a calculator to figure the gas mileage, not dashboard computer. I have even factored in the larger than stock tire size.

I think what hurting my mileage the worst is the fact that the truck keeps shifting between 4th gear, and 2nd gear at 45 mph. As I drive down residential streets, as soon as the road is flat, the truck will drop into 4th and the RPM’s drop to about 1200. This is way below the power band. It will bog down for a while before it drops down into 2nd at about 300 RPMs. It hangs there until it is back up to speed, and then it will drop into 3rd at about 2100 RPMs for just a second before it drops into 4th again at 1200 RPM. Driving about 5 miles on a 45 MPH street It will do this about 10 times.

What is keeping is keeping it from riding in 3rd at 2100 RPMs (a good sweet spot for the I5) at 45 MPH?
 

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Discussion Starter #3
Is it possible the transmission shop that put in the Corvette shift servos messed something up? I know the Corvette servo should not effect overdrive, but could they have put an incorrect spring back in or something?
 

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I have the exact same complaint about my truck. Mine didn't seem to lug as bad prior to having the head replaced under warranty. My belief is that my computer was reset during the warranty work and has now learned how I drive. I tend to drive like an old lady trying to get the best possible mpg I can. It is my understanding that these trucks adjust transmission line pressure as well as shifting strategies based upon your driving style. I only had my truck a few months before it went in for the head replacement, so the previous owners driving style was prob more aggressive than mine, thus the noticeable difference in shifting. My fuel mileage has dropped from 22mpg down to 18mpg. I believe this is partially due to winter gas and running the defrost. I recently changed my transmission fluid, filter, added the corvette servos, and the super servo 4th. This only seemed to make my truck lug in overdrive even worse. I have since removed the SuperServo. I installedmSuperMod's ported throttle body and supersparks to add a little power and try to help my rough idle. Even though the mods seemed to allow the truck to accelerate smoother it didn't cure my idle issue nore give me any noticeable torque increase to help with the shifting. I believe a tune would help my problem, but I'm reluctant to spend the money on a tune, even though that seems to be my only option at this point.
 

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There's two different servos; 4th direct and 2nd direct if I recall correctly. The 4th or overdrive one controls your 3rd to overdrive shifts and the 2nd controls the 1-2-3 shifts, there can be a "corvette" servo for both of these. Depending on what was put where may affect this.
 

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Discussion Starter #6
I will contact the previous owner and see if he know which servos were upgraded.

Is there anyway a bad servo, or a bad install could cause the truck to continue to shift into overdrive at 45 mph?
 

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What is the STOCK size tire for THAT truck? If your tires are too big, there's your answer. The shift points are being influenced by the slower turning tires.
 

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I will contact the previous owner and see if he know which servos were upgraded.

Is there anyway a bad servo, or a bad install could cause the truck to continue to shift into overdrive at 45 mph?
That's what the factory shift point is at below 50% throttle. Get a tune that's the only way to really fix it for good.
 

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Mine likes to lock up tcc about 45mph fail below it unlocks. It wants to lock and unlock about there. Any changes it engine load will factor in in it unlocking and locking.
 

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TIS

Type your VIN in and select the PCM/VCM Controller and see whats out there for PCM updats for your truck, i learned the hard way and wasted money get it updated THEN a nice tune!
 

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Discussion Starter #13
the original tires were 265-75/15 and now I am running 265-75/16. The tires are about .9" larger in diameter, however it seems like everyone else I talk to has larger tires than OEM, but does not have this problem.

I did bring the truck to the dealership last week, and they verified I has all the current software already loaded on the truck.

I know a tune would help, however I want to be careful about masking a problem with a tune. That and I can not find anyplace in Minnesota that does street tunes.
 

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maniac mechanic
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the original tires were 265-75/15 and now I am running 265-75/16. The tires are about .9" larger in diameter, however it seems like everyone else I talk to has larger tires than OEM, but does not have this problem.

I did bring the truck to the dealership last week, and they verified I has all the current software already loaded on the truck.

I know a tune would help, however I want to be careful about masking a problem with a tune. That and I can not find anyplace in Minnesota that does street tunes.

You're not masking a problem, you're fixing it. Since you have larger tires now and haven't compensated for them as well as the shitty factory shift point, this is the cause of what your describing.
 

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I went to the site and checked for updates on my truck. Here is what is listed:
12627883 0000FEEC New software with driveability and fuel economy improvements achived by decreasing the time TCC will be unlocked due to a misfire rough road event.
12606375 0000B534 New software to enable clear flood functionality
12591649 000082DA Operating system

Wouldn't this make my truck lock the tq converter sooner? Maybe this was done with the headswap and caused my problem?

Casey


TIS

Type your VIN in and select the PCM/VCM Controller and see whats out there for PCM updats for your truck, i learned the hard way and wasted money get it updated THEN a nice tune!
 

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Mine wanted $190 and then I ended up getting the updates done for free when my cylinder head went and it made absolutely no difference.
 

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Get the tune. Find a tuner or have one of the guys off the site do a remote tune for you. Yes..not exactly cheap...but they will have a computer in your truck while you drive and be able to tell you exactly what is going on. The tire size your running now should have NO real effect on your truck, much less the shifting issue your having. And the fuel milage your getting really sucks.

Both of these can be helped by a tune, in fact they can change every single bit of your trans shift pattern holding any gear to any speed I believe. So a tune WILL fix your issue.
 

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My question is why do we need to get a tune to make our trucks drive like they USED to. My truck hasn't always lugged like this. I'm sure a tune could help the issue, but it shouldn't be a requirement. My truck seems to downshift on hills some days, and hold in overdrive other days. This makes me think there is a sensor that could be going bad, or atleast reading differently than it used to.
 
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