Again...driving style is a biggie...
The Automatic is an E4OD...I personally dont care for them, but I've never owned one...ridden and driven a lot of them though. They hold up about like any other automatic. WAY better than the dodge 47re though. Put a tranny temp gauge on it and be nice to it and it should handle that load easily.
The manual transmission is a Borg Warner ZF5. Original equipment flywheels for these trucks are giving fits now. They are a dual mass unit and are somewhere around 1300 to replace new. you can buy used but that is a gamble. Many just replace them with a single mass conversion flywheel that includes clutch, pressure plate, throwout bearing, and all the bolts needed with good instructions for 800 tops. LuK is a good name when buying that single mass kit. The tranny itself is good. spendy to rebuild like most. and if someone ran a dual mass competely out before replacing, they may have trashed some synchronizers, usually 3rd and reverse go first. I personally would go with the stick...im not sure what an auto will run you to replace...somewhere around 3,000 bucks? and for 800 you could have a manual that will last you 200,000 if you take off in 1st like your supposed to and would be cheap to replace just the clutch disk if need be. Get the stick.