Be careful how much you do on the stock tranny, they are not real strong.
My suggestion is to go find a used one in good shape and save up to get it built right so that when the current one goes out it is an afternoons work and you are back on the road, then use the stock one to go have rebuilt and upgraded in case the other goes out.
They usually last around 200k or so but towing regularity and driving style are two of the bigger factors, crank it up with a tuner and you add to the potential a bit.
Just a heads up that may save you some headaches.
__________________
"I'll keep my money, guns and freedom. You can keep the "Change."