Regarding the red GMC pictured above it looks like a 1 ton by the front bumper and front axle.
Rear wheels with 10 lugs at 7.25" bolt circle would be an axle from a 1.5 or 2 ton and would physically bolt in with the springs from the larger truck too.
That size bed with even a half load of gravel looks like more than enough for a 1 ton.
