I've got a 2015 GMC Sierra with the 6L80 and it's been flaring between 3rd and 4th for a while now, plus a hard shift when it's cold. A buddy sent me a link to https://gearboxrepairsharjah.ae/brands/gmc/ and said they might be worth a try, but I can't find any real reviews from actual customers. Has anyone here taken their GMC truck to them for transmission work, and did they actually fix the issue or just do a band aid repair? I'm a bit nervous because it's my work truck and I can't afford to have it in the shop for weeks. Appreciate any honest feedback.