The Blazers were listed as "3/4-ton" trucks by the military, but that was because they had roughly a 3/4-ton payload. It was actually 1200 lbs, but what's 300lbs among friends, right?
I have heard that the pickups were 3/4-ton trucks with a 1-ton front axle, but that is simply not the case. For one thing, the VIN is a definitive clue that the trucks are "30 series". Some argue that the pickups were 3/4-ton because most had the NP-208 transfer case, which was only used in 1/2 and 3/4-ton trucks in the civilian market. If anything, the truth is that they are 1-ton trucks with a 3/4-ton transfer case. The NP-208 is pretty darn durable and was much more economical for GM to use than the NP-205 for the contract. The M1031's did get the NP-205, but there were relatively few of them.
My civilian crew-cab V30 weighs about 6200 and has a GVW of 9200 (no overload springs), so it's essentially the same as the M1008, which weighed about 5900 and had a GVW of 8800 lbs. The overload springs of the M1010, M1031 and M1028/A1/A2/A3 variants gave them an additional 600-700 pounds of payload capacity and a GVW of 9400lbs (9450 for the M1010), which is about the same as a civilian truck of the same vintage with the same overload spring option.
M880's, on the other hand, were all built on a civilian W200 (3/4-ton) chassis. But they were not part of the CUCV program.