You've got that right!
Sorry if my post was misleading. I can run 75mph or more unloaded (just Burb, no trailer), especially since I've got 3.42 gears and overdrive. With my trailer empty (2600 pounds), I can maintain 65mph on uphills, and then run 75 or more on flats and downhills. When I towed the TJ (13,500 GCVW) I could maintain 65 in most places, but dropped to 55 and even 45 (downshifted into 2nd gear) on some hills.
Last night I towed a Chevy Celebrity and a Camaro front subframe from Greensboro to Mebane. I kept my speed down to around 60 because I had too much tongue weight and I wasn't in a hurry, and I had no prob maintaining that on hills. The cool thing about the low speed is that the fuel gauge barely moved the whole trip.
Swapping on the non-EGR intake manifold, Banks exhaust (my stock is rusted out anyway) and cold-air intake, and getting better gearing when I swap in my 1-ton axles should help some. I've got all the parts, just need to put them on. But I'm not kidding myself into thinking this is will ever be a powerful motor. If I can get it feel about like a 350 Chevy with better fuel mileage, that's fine with me. A bunch of folks swap on the Banks Turbo kit and say that makes it equal to an older stock 7.3 Powerstroke, but they also can blow oil seals and head gaskets due to the turbo. I'm not going to spend much money on this, because if when comes time to replace it, I'll swap in a 12V Cummins.