Like tbear mentions, you don't state whether your truck is 2WD or 4x4. If 4WD, using the low-range gears might be an alternate option. I recently installed a switch setup to allow me 2WD-LO, and have already used it several times. I, too, have a steep driveway, and while my 19' T/T is well under 7,000#, it's still a great help to have the low-range gears.
I also installed an F-250 trans cooler this spring. Being in the direct airflow of the radiator fan does help at lower speeds (in addition to the larger surface area).