Before I sold my race car and bought a tractor, we towed a 48 ft gooseneck trailer with an F350 and a four speed automatic. We would take two Mustangs, a quad, two large toolboxes, air compressor, generator, etc. It was pretty heavy. We hauled from south Florida as far as Dallas, TX and Epping, NH. We had very good results with the auto, but we purposely tried to NOT kill the tranny. Whenever it started to shift we would lift off the throttle, no WOT blasts from a standstill when the trailer was attached, no cruising on the highway with the boost set to 25 psi, etc. The truck also had two aftermarket tranny coolers running in series, behind the factory tranny cooler. I suspect this increased longevity quite a bit. If you try not to kill it, it should last for quite a while. I guess it depends on the definition of "quite a while" though.