My neighbor just bought a 1995 RAM 3500 with auto trans. It replaces a Ford F250 5 spd. He pulls a 5th wheel that weighs 8,000 lbs. My truck is a 5 spd and I never had an auto so I can. t answer his questions. When pulling the 5er should he shift from 1st to 2nd to D or just leave it in D. Also it has an overdrive. Should he use it or not. Any tips would be appreciated. Oh yeah of course it is a Cummins I didn't mention that thinking it was understood. Thanks alot.