Couple things need addressing here:
1) Please use capitol letters at the begining of a sentence and a period at the end. Otherwise older guys who know what they are doing, and who can give valuable information, just might mistake you for a punk kid. Spelling mistakes are ok as long as you get the point accross.
2) A stall convertor will ease the loads on everything with a off road type of vehicle. It effectively cushions shock loads in this type of application. RPMs of the driving shafts do not equal load. Load equals load. (that probably went over a few heads
3) Your tranny needed rebuilding for one of several reasons. Since fwd went out you either have worn out clutch pacs and/or you lost fluid pressure that pushes the clutch pacs together. It was not directly the fault of 31" tires. However a taller/heavier than stock tire, combined with a heavy right foot, and a stock gear, with stock stall ratio puts increased loads on the tranny. (As well as everything else)
Chances are that the tranny fluid was never or hardly ever changed. Then add the increased loads over time and you have a failure.
Point being.. the tranny shop probably did'nt want to mess with trying to explain all this to you. So they just gave you a short answer that would make you happy at the moment. (welcome to the repair world)
Nearly every tranny failure is due to loads over time and a break down of the fluid.
You can't blame the shop for giving you a short answer. So to say "bs" only serves to further pride heaped on top of ignorance.
If your interested in using the 4x4 in a high performance way.. then accept several things right up front. You will break things. Less things will break if you modify them to be stronger, and take care of them (changing the fluids & filters more often).