If a different grade of gas seems to "fix" it, you are not having a tranny issue. Perhaps you are perceiving it to be the transmission when the engine is the real culprit.

In a headwind, the engine has added resistance to overcome to maintain speed. If there is a knock/predet issue, the engine isnt running at maximum efficiency, and thus is unable to overcome the added strain of the wind; which would slow you down, and make the TC unlock (which would feel like a downshift).

Higher octane gas (premium) reduces knock, which allows the pcm to trim fuel better (when it notices knock, it tries to rectify the situation by adjusting a/f ratio and spark timing, which essentially neuters the truck). Better fuel trim nets better performance, which translates to being able to overcome more resistance.

 

PCM on these trucks don't have a clue if the engine is pinging or not. There is no knock sensor.

 

When I first bought the truck, I though the trany was needing an overhaul. Then I noticed when running premium, for the idea of cleaning the fuel system due to the higher level of cleaners in premium, the truck does not downshift near as much. Switched back and forth between reg. & premium fuel, and with premium the truck does not downshift near as much. For some reason my truck does not run well on reg. gasoline. I do not hear any knocking or see any misfiring recorded.