Sounds like the oil pump died on yours. Try disconnecting one of the cooler lines and crank the engine. Should have good flow.
Good advise. I've had a tranny fail, ( no 3 or 4 ) and had it rebuilt. Bench rebuild was $500, Parts cost me $800 and I had to drop and install; that was 3 years ago. Shortly after it was reinstalled ( a month or 2 ) the tranny just stopped working while highway driving. No funny noises, no codes,...... just quit pulling and drifted to the break-down lane, then wouldn't move from a stop. I had re-used the original 180K pump during the rebuild to save a little $ and my reward for being a little cheap was that I had to drop the tranny again. ( thankfully - it was about the only thing I did "cheap" during the rebuild...! I bought the beast, new TC, shift kit, ect... ) I've also had a pump fail due to poor installation once. It wasn't seated on the shaft properly and broke when the tranny was bolted to the bell. Same conditions,... no noises, showing full, and no codes.
Replacing the pump should be kinda' cheap,..... I'm GUESSING that to put the truck on the lift and drop/reinstall will be $5-600 + 125/300 for a refurb/new pump. If they are quoting you 2K-$2500 they better be giving that tranny a FULL rebuild.