Thanks for your replies.
1st I don't think there is a government calculation for GVWR (if this was true then how could companies like ford increase their numbers without doing anything to their truck?)
2nd The RAWR on my truck is 4150lbs and the FAWR is 3950lbs (total of 8100lbs). The rear is the same on a 4x4 tundra but I can't seem to find the front #'s for a 4x4.
3rd Toyota uses depending on packages the same all season tires on both 2wd and 4wd.
I know Toyota is very conservative with their #'s so I am not too worried (plus I only tow a 4500lbs trailer) but it would be nice to have some more room just in case. I think it is all marketing unless someone can prove me wrong:)
Don.