[rickst29]

John, I'll drop my 4Runner shift selector to "4th" when towing on grades (even moderate grades, less than 3%). And on big hills, my Toyota's shift points don't downshift as early as I'd like -- I basically run it as a manual, keeping it at about 300 RPM's higher than my V6 would choose.

I know that your Tundra, in comparison to my 4R, is massive overkill for a 2619. (Until you get into the mountains, which is pretty quick in COS -- or in Southwest Reno.) Since they did give you a special "tow" button, it probably does everything I do by hand -- disabling 5th and downshifting more aggressively. Unlike your button, however, I'm very comfortable with 5th on level roads and slight downgrades (those which don't need a lower gear to provide a just a bit of engine braking.)
- - - - -

For everyone, I point out a simple fact: When you're stomping the gas peddle way down to "lug" up a hill with your Trailer, you're getting worse gas mileage than revving the engine in a more favorable range. (It doesn't just wear your Drive Train components, it costs you at the pump too. They didn't program the Tranny computer with a trailer in mind-- it's optimized for gas mileage under EPA testing conditions.)

If you don't get a good power response when you push your foot down a bit more, you should probably be changing into a lower gear.