I have a 2004 Tundra with the 4.7L V8 & towing package. Max tow rating is listed in the owner's manual as 7,200# for my truck's configuration. GCWR is around 11,000#. Last time I hit the scales, the truck (loaded with 2 dogs, family, gear, full fuel load, & trailer hooked up) was about 6,000#; trailer was a 2,400# pop-up. GCW was 8,400#, leaving about 2,600# available. I get the same fuel economy towing as empty (but I'm easier on the gas, speed, & brake when towing). Very comfortable with this setup. I can get 300-350 towing miles on a tank of gas (21-22 gal).
I've towed a 5,000# moving trailer without any problems. It sure did notice the fully loaded 6x12 U-haul though! I made sure the bed was mostly empty (only a few light items in it) because I was probably right at the max GCWR. It was in-city towing with lots of start/stops and max speed of about 55mph.
In short, I love my Tundra. It fits MY needs without being overkill. I would not even consider towing my father's 28' 5er with it. For that I'll use his brand new F350 V8 diesel...