Honestly, I would get one from the junkyard. You can rebuild yours but these trannies are pretty stout. You might want to price out a rebuild first.

As for upgraded tranny's, we really don't have one available to us. There are upgraded parts for the diff (like diff pin savers and Quaife's) but really not much to choose from. There is a gentleman on neons.org who is doing some kinda neat things with tranny's. I think his rebuilds start at $900 plus shipping.