Need truck advice

My 4.7 Durango (2002) 3.55 gear struggled a bit with my single axle 3600 pound boat from the stops. Once it was moving it wasn't a problem, even long distances.

My '05 Ram 1500 5.7 has no issue with it. Like everyone says the box rusts in a heartbeat. You can hear it rusting on a quiet night. The box wheel wells only had a small plastic flaps in front of the wheels for crud control so I had to buy full liners for it. Too late for the rust though.