[NHRABill]

After reading majority of the thread (skimming some) I did not see anyone mention converter lockup speed. Flubbing around with tire and gear size is one thing but ignoring the trucks cruising engine speed and converter lockup rpm is leaving a lot of fuel burned up with no benefit.

Look into a electronic lockup kit for your transmission. The typical stall converter (at least GM from years past) was 1200-1500rpm before lockup. As was already mentioned, lugging the motor with tall gears and a big tire is wasteful. When the cruising speed is below 1,800rpm you risk slippage wasting power and fuel. I installed a couple B&M trans lockup kits years ago on 700r4 and 2004r transmissions I am sure they should have something similar or better today.

I reduced my tire size because I rarely drive on the highway almost always in town heavy traffic, My trans shifts into 4th around 45 mph. full lockup happens closer to 50-55mph. better than it was and sweet spot for cruising around 1800rpm is close to 65mph.

I think I just did the long way of saying pay attention to your torque converter more so than the other items mentioned.