94 E420 Tranny?

Hello There,
I haven't been here in a while ! and actually I wish I didn't have to ask his question ! My tranny is slipping !it is full of tranny fluid ! It started a few days ago ! it was shifting hard and now when i want to get on it a little it's not catching the gears ! if I drive it lke my grandma would it's ok ! Is there anything that could cause this other than it's about to go out? My 96 Chevy truck was shifting hard once and found out it was a fuse ! I have a buddy that is a MB mechanic and he told me if it is tranny that I might as well get about $2800.00 lined up ! I figured i would ask here first! if it is a tranny and can be rebuilt what does that normally run? or is that not a good idea?
Thanks a Bunch !
Bob