[08Canyon]

Smoke at startup is generally oil leaking past valve seals.

 

[08Canyon]

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.