The difference between the tran's strength wise is just the diff. However some gtp people like to switch to a gt trans for the 3.29 gears, 3,000 stall converter, and the only thing they have to do is switch the gt diff for the hd diff found in the gtp trans. Its a great cheap upgrade for a gtp but still neither trans really has the strength to hold low 13's and faster. There has been people like ron vogal that have run 12.14@114 on a stock trans but his car has quite a bit of work done to save weight. The lighter the car the longer the stock trans will last depending on power levels.
If you decided to do a top swap and get the gtp heads, blower, manifold, ect, it's actually better because of the compression ratio. A lot of people like running the higher compression bottom ends so they can make more power. It's great for our inefficient blowers since you don't have to run as much boost it's all timing from there. Maybe something to consider down the road so you can basically have your gtp back with a little more umph. All you gotta do is get a gtp diff and swap them out which is cake imo.
