Going to try for a new tow vehicle

UPDATE ON GAS MILEAGE:
Made a 90 mile trip this morning.
At 65 mph it runs right around 1500 RPM and gets about 20 MPG.
At 75 mph it runs at 1750 RPM and gets about 18.5 MPG.
The truck now has 250 miles on it, definitely not broken it yet, so these mileage figures are very encouraging!

Also, I had someone tell me to have the jake brake turned on even when I'm not towing. Your opinions on that.