I just purchased a 2005 V-6 Tundra SR5 extended cab truck, The second day I had it I drove it to work. One of the guys I work with pulled in behind me and we all gathered to inspect and look at the new addition to the crew. He noticed the rear passenger side of the bed appeared to be lower than the rest of the truck.
Upon further investigation with a levell we dicovered the whole truck does twist down on the right side rear.

First thing I did was contact the salesman and notified him of the problem, he said just let the service department know about it when you get your 2500 mile oil change. To make a long story short the service department could not find the reason for the strange drop or twist in the bed. They contacted Toyota Corporation today and discovered that this was a known issue with the Tundra, so now its going to a body shop to find out what can be done about it.

I hope its not the frame, apparently this truck is the worst one they have seen. I would say it drops almost an inch. Stand in the back of your truck and look at the top bedrail compared to the line on the back of the cab and see if it matches! I will post results when I find out what it is. I love the truck its great I just hope this is something they can fix.