You "see" a lot of things on the road. Doesn't mean they should be emulated or copied.
Take safety and "the numbers" right off the table. You're not going to be unsafe if you get a 5th wheel with a 2000lb loaded pin weight for your Tundra. It's way over the payload numbers for the truck, yes, but there are safety factors built into all the components on the truck. Barring a freak accident caused to a microscopic flaw in your equipment that would go unseen by the human eye in the most thorough of inspections, you will get from point A to point B.
The question is, "Will you be happy with it?" When you get to overloading trucks like the Tundra, the likelihood of you being truly happy with the rig after the newness wears off, goes way down. Slow, squishy, sluggish... and you'll get sick of it right quick. Then what? You've got 10's of thousands of dollars invested, and now you have to spend tens of thousands more on a bigger truck, or take the hit and trade for a smaller trailer.