My 2001. 5 4x4 dually was the best truck I've ever driven in the snow, and I've driven a lot. I hope my 2003 SRW will be the same, but the roads haven't been sloppy enough to really tell yet. One thing I can't say enough - if you have a dually, get the limited slip.
Nothing ever stopped that 2001, it just cut right down to the pavement. Never got it stuck in mud either, although I was always cautious (especially when towing a trailer through mud).
I had an 11' flatbed and a 38 gallon aft-axle aux tank in it, so I never carried winter weight.