bowler1, are you asking for responses just from other Toyota owners?? Because you are going to get numbers that are all over the place.
My 2008 F250 with 5.4 V8 gets 10.5mpg towing our 21ft ultra light at ~67mph. That will go down in hilly areas.
Engine "mods" will rarely get you better miles per gallon - you might get more power at the same mpg, this can be great for towing. Which, arguably, is "better" mpg depending on how you play with numbers - you could say you are getting better "miles per horsepower".
Cruise control can help you to "smooth" out your mpg, and also (for me at least) help greatly with long drives. In hilly areas it can be better to shut off cruise control, as you can anticipate hills that CC can't. I find my CC waits far too long to downshift, then routinely downshifts two gears to keep up speed. By temporarily shutting off CC (by easy tap of brakes usually) I can speed up and/or make the transmission downshift early at the base of a hill to make it easier to get up it.
This is where bigger engines, especially diesel, shine. With more power, they don't have to downshift as often, meaning they routinely run at lower rpm while towing - which translates into better mpg.
This is a simplified explanation for something that can get as complicated as you want -- just search these forums for threads on mpg!
In the end, if you are satisfied with your rig, just go camping!