What year is it? Cab & Chassis models should have available wheelbase info online
Any RPO codes in the glovebox? Those codes may shed some light or run the VIN by any local GM dealer and they should be able to tell youI definitely plan to treat and undercoat the frame. The truck has been in FL its whole life, not sure of what they had in the dump bed tho. Mostly surface rust, no real rot.
Still trying to figure out the easiest way to determine whether or not this thing is a 159.5" or 183.5" wheel base. I know its not 135.5" cause its not a stubby.