they are a good tranny, mainly when you find a good builder.
just find a good builder to build a 700r4 and it should last you. they can be beafed quite a bit, but it does come at a price, usually around $1000.
if you want to go threw the hassle, you best bet would be a 4L80E, but you need to change tcase (or input), get the correct adapter, lengthen/shorten driveshafts, and get a standalone computer. they are $$$, the tranny and the comps