I have the same issues. I had the dealer apply the alleged fix with no discernable change. I am tending to believe you may be on the right track. I plan to try running a few tanks of premium fuel to see if anything changes.
I have the same suspicions.
I would like to have some proof of the application of the TSB since the person at the dealer looked at me like I was from outer space when I told him about the TSB.
Agreed, I am also waiting for a real solution. I love the truck with the exception of this issue with the transmission shudder in the higher gear ranges.
I also had the TSB fix applied. They only reprogrammed the PCM. Shudder is still there but not noticable in 8th gear, mostly in 10th under light load. Under heavy load it will downshift and reduce the shudder.
Unplug the dummy portion of the connector. If you don’t know how to do that, ask a local mechanic to show you. It’s a matter of compressing the tan that retains it and pulling it out of the wired portion of the connector.