So about a month ago my 2015 Yukon Denali started doing that thing where it felt like I was driving over a cattle guard every time the torque converter locked up at highway speeds and my regular guy in Dubai said he could do a fluid flush but he wasn't really a transmission specialist and recommended I either go to the dealer or find a dedicated gearbox shop, and since the dealer quote for a new 6L80 was basically the same as a down payment on a new Yukon I figured I had nothing to lose by trying one of these Sharjah specialists everyone keeps mentioning in the Facebook groups. I found this place https://gearboxrepairsharjah.ae/brands/gmc/ and called them up and the guy on the phone actually knew exactly what I was describing with the shudder and explained it's a common issue with the torque converter clutch material breaking down and contaminating the fluid, and he said they do a full flush with the updated Mobil 1 synthetic LV fluid and if that doesn't fix it they can rebuild the converter in house for a fraction of what the dealer charges for a whole new unit. Dropped the truck off on a Thursday morning and by Sunday afternoon they called saying it was ready and the shudder was completely gone after the flush plus a software update to the TCM, and I've put about two thousand kilometers on it since then driving back and forth to Abu Dhabi and it's still smooth as glass which is a massive weight off my shoulders because I was mentally preparing to sell the thing for scrap. The shop itself wasn't fancy like a Dubai waiting lounge but it was clean and organized and the mechanic showed me the old fluid which looked like used espresso so I'm pretty confident they actually did the work and didn't just reset the adaptations and hope for the best, anyway just wanted to share a positive experience for anyone else with a GM truck that's starting to shudder on the highway.