If i'm not mistaken, The '55 2nd series, & up 350, is indeed a 2 ton, then you have the 370 series(19500lb. gvw), which I think is considered a 2 1/2 ton, then comes the 450 series,(22000lb. gvw) which would be a 3 ton. I'm not as sharp, on these late model GMC's, as I am on the earlier '47-'55 1st series Advance Design(New Design) Trucks. I know with them, a 350= 2 ton, 400= 2 1/2 ton, 450= 3 ton, & 470= 3 1/2 ton.
