If it still has the ID plate (picture below) and the cab is original to the rest of the truck the serial number will tell you 1/2 ton, 3/4 , etc.
10x22xxxxx is 1/2 ton 15222xxxxx is 3/4 ton 25x22xxxxx is 1 ton
I use my mostly stock '52 3/4 ton for work around my place as well as trips to town and occasionally further. It is scheduled to go to Austin (90 miles) in a couple of weeks to deliver some excess furniture from our house to a nephew who is just setting up housekeeping.
For more specific GMC information, I suggest visiting OldGMCtrucks.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12 '52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
