My dad is the original owner of a 77' Ford F-150 custom 4 wheel drive. I have pulled some heavy loads with that truck with no problem. I have even pulled mobile homes up steep inclines. It has a 351 Modified with low range and high range 4wd.
I did have a universal to go bad on the rear drive shaft while pulling a heavy trailer loaded with a car up a steep gravel mountain road. I sat there and held the brakes for 15 minutes and then decided to let it roll back into the ditch to get stopped.
