Considering tow ratings are not legal ratings, only warranty ratings......probably not a LOT of difference. Unless a gear change, many HP change, or some other MAJOR drive train difference occurred. It will more more of a , did the newer versions bells and whistles suit your rear end!
I'd pull 15-20K with my 05, it was not rated for that! It had not issues running down the road at 25K total, gcwr was 23500 for the dually models at the time. 30K total would not have been too bad, other than lack of low gearing for steeper grades at slower speeds...ie camp grounds, 18+% grades here in the seattle area I go up! I'd be stalled out blowing up the allison transmission!
marty
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
2014 Chevy 1500 Dual cab 4x4
92 Red-e-haul 12K equipment trailer