I got a 21 gmc sierra 3500hd regular cab 8ft bed srw 4x4 sle, the difference between 2500 & 3500 is the 3500hd comes with a more heavy duty rear end 12inch vs 11inch on 2500hd and 2 overload springs on 3500hd the rear end on a 2500hd is only rated for 6600lbs while the 3500hd srw is rated for 7250lbs which gives higher payload capability slightly higher gooseneck capacity, while conventional towing is the same as 2500hd gas standard tire on 2500hd is 17inch vs 3500hd is 18inch otherwise both are identical