F650 as 5th wheel tow vehicle.

Lightning Driver, I would keep the 7.3 and do some power mods. I have a 99 7.3 and am towing a 40ft 14k trailer and do it with ease. I used a HFSB turbo kit from DP Tuner along with injectors, upgraded high pressure oil pump and a tuner with multiple settings. I also added a 4" turbo back exhaust, and improved the fuel system with new high pressure injector lines, air intake and other minor parts. It changes the truck dramatically, I can pull just about any grade at 60mph and exhaust temps under 1200 easily passing just about anyone I want anytime I want. I spent probably a total of 5k on the mods and it is extremely reliable. Towing I use 3 different tunes 20/40/60 hp depending on terrain and weight I am hauling to help keep exhaust temps down. Non towing I mostly use a modified stock tune and it drives like a gas powered truck I have to watch my lead foot as i find myself chirping the tires in 2nd and 3rd gear. I looked into all three major brands of new trucks and was thoroughly disappointed with the power and torque when I drove them. I am so happy I did not buy a new truck. Oh and I am towing with at 3.73 rear gear.

Steve