[Jackpine]

This is SO strange! You have nearly the same truck as me, and with UD pulleys, you ought to get better mileage. I get about 15.5 at 70-75 and I never got that much before the custom tunes. I have the 200#+ bed cap that sticks up about 6 inches above the cab, so it adds wind resistance, as well as weight.

I NEVER feel any "drag" on the motor, and here in Arizona, the climate control is ON - all the time!

I WILL say, and I almost hate to bring it up, but hot temperatures are better for fuel economy than cold ones. And, it's not due to the blend of gasoline. It has to do with the A/F mixture and the fact that cold air is more dense, needing more fuel to maintain stochastic (which is controlled by feedback from the O2 sensors in closed loop). Anytime you run in hot temps or at high altitudes, you should expect a loss of power, but an increase in fuel economy.

This simple fact is why aircraft fly at high altitudes when traveling long distances, whether they are jet or recip powered. (For short distances, the climb to altitude is such a gas guzzler that they stay low).

And, going back to your first post, which I somehow missed before this, I DID reduce part throttle upshift and downshift speeds by the max to get my truck into higher gear sooner and I did the same with the TC lock/unlock points (trying to keep the TC locked as long as possible). All this was in the name of trying to keep the transmission from downshifting/unlocking when it felt like there was still power to spare. You could always try this - I don't see how it could hurt.

- Jack