Need advice for all-around truck that can tow

My dad's 93 3/4 ctd 4x4 with 5spd is still going strong and still pulls his boat or car trailer and nova wherever and whenever he wants. He's the original owner and 99% of it's life has been used in towing and not as a daily driver. The original Getrag is long gone an been replaced by a nv4500 some time ago. But that drivetrain will outlast that truck and frame as a whole. It just won't quit. As said, anything first gen cummins would be your best bet