This article is from the Toyota Tundra FAQ, by Steve Yee with numerous contributions by others.
Well, this is another one of those things that Toyota Engineers felt that they
knew better than the consumers did. The Tundra doors does not have an adequate
roller notch, or "detent" in which it will "stop" the door one thirds, two
thirds, and fully open. There is no fix for this, and there will be no major
changes for the 2001 model year. The 2001 model year Tundras seem to have
quite a bit more friction, but owners of 2001 Tundras have also complained
about the lack of detent friction while parking on inclines.