If I were thinking gas engine in a 3/4 ton I'd save the money and just buy a newer Tundra. Actually 120,000 miles on a Tundra isn't a lot of miles.
The Tundra is a beefed up 1/2 ton but it's not a 3/4. If you have a load to haul, you need a truck made for it, not just advertised for it.