Wanted to wait a couple days before posting an update but this looks to be fixed for me. Ultimately it was a differential fluid issue, which is one of the shared fixes across the threads in this subject. I have the 3.92 rear end with LSD. What I’m struggling with is how difficult this has been to diagnose by the respective dealers. Dealer #2 was much better at diagnosis, listening and ultimately solving the problem. I equate it to just seeing more vehicles and having more tenured staff and mechanics than the 1st dealer. Tracing this all the way back I had zero issues for the first 16k miles or so. Towed a boat and launched and recovered at a very shallow ramp which had the rear end submerged for >5-10 mins. They shared that this was a potential introduction of moisture to the fluid, which makes sense cause I had the issue for the subsequent 3k miles and upon seeing the fluid they said it had bubbles in it but was not milky at all. You drive so often you become numb to changes over time but I can tell you this has also fixed the surging when letting off the brake or restarting from stop/start and the truck is more stable when crossing expansion areas on the highway like bridge transitions. They also suggested doing the rear differential fluid service every 30k miles anyway having seen other issues, especially those that tow more. Hoping this helps others experiencing the issue.
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