You're right about that. The 2500's still use 4th gen (DS) sheet metal, and 4th gen rambox design. Ram changed vendors for the 5th gens (DT). So the 2500 and 1500 ramboxes really have nothing in common but the name.My son has a friend with a 2020 Ram 2500 with Ram Boxes and the alignment looks like it's still true from manufacturing. But I think the box contour of the 2500 is different than a DT and not of the same mold, maybe not even the same supplier.
Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 03 June 2018. Now at: 049108 miles.