For that much weight in CO you want a diesel. For that much weight in general I'd get s 350/3500 series truck for sure. There's no advantage to getting a 250/2500 that I'm aware of, at least not any advantage worth considering. I guess in a RAM the 2500 gets you the air bag suspension. I haven't driven one but I would want leaf springs for hauling that much weight. There's less to go wrong and loaded up it should ride just fine.
If you want a truck not above 10,000 GVWR for insurance purposes I know that at least GM will sell you a 3500 SRW, normally rated at 11,500 GVWR, but only rated at 10,000 to dodge some of the legal requirements. It's the same truck. This also illustrates how silly the argument is about the GVWR being the end-all-be-all of truck ratings. They play games with it depending on the laws.
