They are the same.

Originally Posted by Grigg
If you have to, the cabs are all the same until the really big trucks, the tractor trailer size ones get bigger. For the 1/2, 3/4, and 1 ton, all of the sheet metal is the same, with the obvious exception of bed and running board length. Fenders, hood, grill, and running boards change, but are the same for the 1.5 and 2 ton.
The GMC trucks bigger than 2 ton have larger fenders and such, and eventually, the biggest ones everything is different.
Grigg