X2
I got my tranny (4L60E) rebuilt a couple of years ago to my specs and the parts I wanted. Original cost would have been about $1700 and ended up costing me $2200. This included cracking open the transfer case to make sure everything was alright and replacing the seals.
I'd suggest calling a few, if not more, shops and ask them what they know about your transmission, what they would recommend as far as beefing it up and what it would cost. If the first thing they say is, "Well, we need to open it up first before we can make any recommendations" hang up and call the next shop on the list.
And whatever you do, DO NOT go to the dealership! The service dept specializes in warranty work, recalls and maintenance. They are not tranny specialists. I wouldn't be surprised in the least that most dealerships send out transmissions, along with other items, to be rebuilt.
As far as a Jasper goes, I know their engines are very good but I don't know about their trannys.