06 2500 auto with 166k. Completely stock.

I did a fluid and filter change and adjusted the bands 5k ago when I purchased the truck due to no record of it being done, and because it had a slight burnt smell to the fluid. Have had zero issues with the trans up until this point. No slipping, shuttle shifting, overheating, etc. Truck was literally fine one minute then not fine the next.

I left work and drove to the gas station with zero issues, fueled up and left the station and the truck would not shift out of second gear. From a stop it would go in first gear to about 2500 rpm then shift hard into second, then wouldn't shift into third. After about 5 miles it finally shifted into third then into OD. Got home, shut the truck down and let it sit, tried driving it again and now it will not shift out of first.

I have no CEL and no codes. I have dropped the pan and the fluid is clean with a slight burnt smell, but there is no debris in the pan and the magnet is very clean. Searching has led me to the possibilities of the governor pressure solenoid or the speed sensor gone bad, but discussions of commonly associated problems with these do not match my symptoms. Any insight would be greatly appreciated.

Duane