I would say it depends on what you do with your truck. If you are planning on plowing snow, towing heavy, or adding a bunch of power I would go with a fully built transmission from one of the sources previouly mentioned. If you occaisionally tow/daily drive a good rebuild from a local shop with a triple disk torque converter, sonnax valve and shift kit will do. You can also upgrade the entire valve body if you want. I would also add a larger aftermarket or late model cooler as well.
Scott