I think when MP said the 2500/3500 frames were wider, he meant 2500HD/3500. The reason is, this is primarily a GM Diesel site, and the late 2500's (1999+ GMT-800) did not have an available Diesel. The Duramax is/was only available in the 2500HD and 3500 (and the 4500/5500). The late model (GMT-800) 2500's are only available with a 6.0L gasser. The 2500HD and 3500 are available with the Duramax, 6.0L and 8.1L. The 1500HD was only available with the 6.0L gasser, while the 1500 can be had with the 4.3L, 4.8L, 5.3L, 6.0L (Denali, C3 and Caddy), and now the 6.2L gasser in the Denali, C3 and Caddy. That's not the end of the story, but enough for now.

Still confused? It's not my fault. GM did it. Not me........

You can stuff a Duramax into anything........given enough time and $$. It will fit into any full size GM truck. The problems surface with accessories and making the engine talk to the rest the truck, and vice versa. It's all workable, though.