I once brought a squarebody Suburban home on a trailer, pulled by my stepmom's '91(?) C1500, on about a 350+ mile trip. I took it -really- easy in D, not OD, and was surprised it made it. Dad being a former transmission builder/shop owner I guess he had more faith in it than I did, or just knew he'd be able to R&R it quickly if it croaked. It was the truck we had available at the time, not what I would have chosen had there been other options. These are light duty transmissions, not built for towing.
Edit, huh, just also realized that same truck took me on a much longer trip with a tow dolly to bring back a Mitsubishi Diamante from a police auction. I think I've tried to selectively block that memory as it was not fun. I'd gone from TX to GA to pick up a pinball machine from a friend. That was nice, but I injured myself breaking down the machine for travel, then had to carefully wrap it and load it with a messed up hand. Then to AL for the police auction and get the car loaded. Cars at the lot were packed like sardines and the Diamante didn't run. Had to push it several car lengths by myself, only able to open the door about 1 foot, and couldn't roll the window down. Get it up to the dolly and load it using a come-along, then the trip back to TX hoping the trans wouldn't pop.. jeezus what a run that was.
Richard