little help plz 88sub trans problems

I have an 88 sub 454 3/4 ton 400turbo . well a couple years ago torque converter to flywheel bolts worked loose and tore up fluid pump. I droped trans replaced pump filters fluid had trans flushed put in new torque converter put the whole thing back together worked just like new . now the bad part I wasnt towing anything with it back then . so i bought a real cheap torque coverter . well now i have a boat and a camper that go to the lake from time to time . when i did tow with it before the pump failure it towed great 70 mph all day long . now with new torque converter i wont go over 55 cause it starts to heat up . also when you start it up after haveing not run for a week or two when you put it in gear it wont move for a minute or two . but i can still drive it with no problems when not towing . . wanting to replace t/c but not sure what to get do i need a high stall for good accelleration or a low stall for good lock up in t/c any suggestions would be helpfull.