Older 7.3 Deisel vs. Newer Ford Engines

A very interesting discussion. In my situation I have a 7.3L 2001 F250. It has 181K miles on it and has been chipped. Also has a recent upgrade on the torque converter and a larger trans. cooler with temp. gauge installed last summer. I agree that a new truck does not make sense when the old one runs great and until now has done the job. And it's paid for. Not concerned about getting to the campground first or fuel mileage ( 11 mpg in town) as much as increasing torque when I go over mountain passes and hills doing a double trailer pull. I go to Colorado with my UTV loaded on my 12' flat bed trailer and it adds another 2500 lbs to the 12000. I take my time out there on the highway but reserve torque would be nice and thus my direction on changing gear ratio on the rear diff. to a 4.3 from a 3.73. That conversion will run me about $900. Any thoughts on this combination with a 7.3L would be appreciated.