I have a 5.0 Screw with a 6" Fabtech lift and 35" tires. I know that will directly effect downshifting especially with the 3.31 gearing. What I want to ask is when I am at high speeds (70-85mph), will the amount of down shifting to 4th and 5th gears that is happening burn up the transmission? I have not pulled a load yet. This is just normal highway driving. Should I be worried about pulling up to 5K lbs? I will never pull more than that.

 

Shouldn't wear it out materially faster. Just may be annoying to some plus significant overall power loss. 5.0 needs to rev a bit for power so 3.31 gears plus bigger tires slows it quite a bit. If you are worried regearing will help a lot.

But the shifting won't hurt the truck. If you tow heavy it could add some strain though.

 

if it's bad you might want to lock out 6th as a start...
then a re-gear might be something to look into...

 

OP - did you correct your speedometer for the change in tire size? If not that may help?

 

Adjusting my speedometer after lift and tires helped out my shifting in my truck with 3.31s between the 45-60MPH range.