I have a 90 7.3 F350 with an ATS turbo, and an 89 F150 with the 351. Both have automatic transmissions and extended cabs. I live at almost 9000 feet in the Colorado Rockies. The 7.3 diesel is far superior in both pulling a load and fuel economy. The diesel averages around 16 MPG where the 351 will average around 11 MPG. With what you are hauling, I think you would be very happy with the diesel truck trade.