When I am towing my boat (about 4000 pounds) I use the sport shift mode so I can keep the RPM's where I want them. If I am on the interstate for extended amounts of time and I can set the cruise at 70 I will put it back in Drive and leave it. It does not have any problems at that speed since the motor is turning more than 2000 RPM's.
With my old 02 with the 4.7 I towed a my car trailer and race car, about 5000 pounds combined and just turned the overdrive off when doing so. I had no problems, tow liked that for 3 years almost once a month
I tow about a 2200lbs trailer everyday, no problem really other than some big hills, and the gas mileage isnt so great. I just drive it like I would if I wasnt towing, not sure if thats good or bad. But its worked for 5,000 miles thus far.
TundraTalk.net forum offers the most comprehensive collection of Toyota Tundra information. Find discussions on the Toyota Tundra Diesel, TRD Pro, SR5, lift kits, towing capacity, classifieds, and more!