Did they put their "assurance" in the purchase contract?
You'll find a lot of variables depending on how the truck is optioned (w/tow package or not), what axle ratio, crew cab or not, etc. Payload capacity, hitch capacity, tire capacities, tow rating, tongue weight, axle capacities, GVWR, GCWR. These all come in to play. You'll have to track down all these numbers.
Some will say to hit the scales or the world will come to an end and that's good advice at some point. It sounds to me like you're just trying to gather some general information right now.
Hopefully someone with experience and knowledge of the Tundra will chime in soon.
