[mikebte]

I have an 08 with 150K on the 5.3. I have done a lot of towing my 33ft RV around the country. At 115K I turned off AFM because I did not like how it turned on an off with towing but never had an issue with it.
I would opt for 3.73 gears as my 3.42 gears keep the RPM just low enough to bug me towing. I also have the 4 speed and here that the later 6 speed was a good improvement in towing. No experience, only word of mouth. My 4 speed has worked great with a transmission cooler. Also, if you can purchase a truck with the trailer brakes installed on the kick panel it may be better. I always wish mine had that for a cleaner look, but I have heard some people dont like it.
I have never ran E85 due to never seeing it at a filling station but over all the truck has been good. The tire pressure sensors usually go out before 10 years but its possible someone could still be running them , they get spendy to replace.
I had both the rear window motor cables go out at 8-9 years of age (easy fix).

Replaced all the brakes and lines at 8 years of age and new fluid, same with transmission fluid. Mine is an LTZ. I have heard of A/C mixing doors becoming an issue but mine still work and I live in Tucson and use the A/C a lot and never mix in any hot air.

I have the cast Iron block and aluminum heads. Not sure if Iron is better or not, I have one broken manifold bolt that I have not repaired, no leaks and I still pass emissions every year.

Overall I am happy with the truck and repairs have been at a minimum.