Something is wrong!! Did you make sure the end of the probe wasn't bottoming out on the casing? My trans cooling system holds just shy of 5 gal with the 6.0 cooler, it takes 20 min of driving before mine moves. normal trans temps range between 70-90 above ambient, the lesser unloaded the higher when toting a load. I think you may still have something wrong. Pull the probe and see if it was hitting the casing, put some washers on it if it was to pull it away.
NCH