With the miles you have stated and the possible pecker tracks of other people under he hood, you could have any number of things going on. 2 things check battery cables and clean maf. What's a 200k mile Colorado cost these days? Good luck.

 

It looks pretty well unmolested under the hood. Ill clean the mass air this weekend. I paid 6700, kbb shows 8700 or something for private party.

 

The way the intakes are made, vacuum is pulled right into the intake from the top of the engine. Shitty design, but that's how GM designed the truck. You probably noticed the little hose under the resonator box that is used for this.


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Yeah i knew that sound was supposed to be there. I was just saying how they say when its clogged that the sound will not be there and oil can be drawn into the intake and cause smoking on start up, more commonly after just taking longer higher speed trips to build the pressure.

However mine has the vacuum sound and exhibits the other symptoms as well, may be almost clogged or something.

 

Smoke at startup is generally oil leaking past valve seals.

 

I have a 900 dollar receipt where the previous owner just had them replaced about 2 months ago.

 

Is the truck factory ride height and tires? I know that the TC locks in and out a lot more when you have larger tires or lift. You can be doing 70 mph on the highway and a slight incline comes up and boom RPMS shoot up

 

It is factory ride height, but has 31x10.50 tires. This does it on flat land going sixty barely using any throttle and will cycle on and off multiple times per minute.

Thanks for all the responses guys, keep them coming.

TJ

 

Mine does the same thing running 31.5x10.50s and with the upgraded servos. A tune would help. I am a 4cylinder tho. I noticed a huge difference and some tranny slip running 32x11s on 20" rims. The tranny would downshift if the wind hit me


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Yeah our trucks go WTF Happened! when you put larger tires on lol

 

31's on a Z85 is a tire size 7.3% larger than stock. That's a lot in terms of computer calculations. Plus it's wider than the P235 (9.2"). If you have a 2wd you likely have 3.42 gearing. That's quite high for 31's.

Your user name identifies you as Z71. If you truly have a Z71, the 31's are about stock size so tires aren't really a thing to factor into this equation.

I can't explain the manual driving shifting, but remember the job of cruise control is to maintain speed at all costs. It will do what it has to do to maintain. That means moving the throttle around and shifting if necessary.

I had a truck underpowered before. I got better mileage driving manually over cruise control because I could control the throttle position.

 

It is a Z71 and does have 3.42 gears.

 

Yep, converter unlock is based on speed and throttle. With o/s tires
1) the computer thinks you're going slower than you are
2) it takes more throttle input to move the big tires

 

Have 2005 5cyl crew z71, had issue with surging 200-500rpm @45-50 like it wasn't finding right gear. Later it would do same @ 60 & 70mph. researched everything , new plugs & coils, TB cleaning, even had tranny checked out.
Embarrassed to say after all that it was low on atf,.(I actually checked not Aamco), added about 1/2qt to get to level, problem went away!
you've got to be kidding me!