I've been dealing with a harsh shift from first to second on my 2017 GMC Yukon for months, and the dealer kept pushing for a full rebuild at nearly 15k AED which I just couldn't justify. After reading a few local forums, I took a chance on a place recommended for GMC Gearbox Repair Sharjah, and honestly I wish I'd gone there first. They diagnosed a worn separator plate and a couple of sticky solenoids, did a full valve body service and fluid flush, and the truck shifts like butter again for a fraction of the dealer quote. They even showed me the old parts on the bench so I knew exactly what failed. If your GMC is acting up, don't automatically assume the worst, find a specialist who actually opens up these 6L80 boxes instead of just swapping the whole unit.