you should rethink your posision on this swap for a min.
if you truly think your driving style is killing these trannys then you will find yourself very sorry you did the manual swap as no 5spd (& 6spds aren't much better) come anywhere near the strength of a 4r70w, if you think it's you thats breaking them, you may as well buy a truck load of t45/3650/etc's cause you'll need them.
I'd venture to say that you didn't get a quality rebuild on this (ie the 2nd) tranny & thats why it also failed.
that being said, there are tons of guys looking to go the other way (ie manual to auto), you can most likely find someone local that'll swap you (with you haveing a bad trans, I'm shure some cash would be involved, but it still might be the best route).