Transmission on the 2012 GMC Sierra 1500 gave up on us 200 miles from home over the weekend. About 145K miles on the truck, not towing during the trip, just running to pick up some stuff. Transmission and differentials were serviced a couple years ago at 110K miles. Just the 1750RD (4400 GVWR) towing during the summer. Weekends and a few long trips here and there. No transmission issues before.
The six-speed 6L80 started having trouble shifting on the high end and I had to baby it getting back up to speed after slowing down through towns. Seemed fine when it finally got up to speed. Used the throttle to keep the engine from over-revving and limped the few remaining miles to the BIL's house. According to the digital transmission temperature readings, it wasn't overheating or anything, about 130F with occasional spikes to 160F when it was struggling. Checked the fluid and the level was good, a little on the brown side but nothing alarming. No shavings on the dipstick.
Stayed overnight and tried it again in the morning. Got a little movement in drive and reverse and then nothing. Borrowed the sister in-law's F150 for the trip home. Called the local GMC dealer (local to where we left it) this morning to get on the service schedule and towed to their lot. Probably won't learn more for a couple days. Was checking online and they do have some nice, low mileage, used 3/4 tons on the lot.