I went from the LTD 20" rims to a 18" Fuel rim, because I wanted more sidewall for an even smoother ride. The tires I went with are Falken Wildpeak. So far, the combination is working very well! The combination rides much smoother than stock, and while hard to tell if it's quieter, the tone is lower so to me the sound is much better for longer days.
Here are a couple of things you mentioned that I will reply to:
- the stock tires are likely Firestone E rated, with a load capacity of 3640lbs. The Falkens are higher rated at 4080lbs. I'm not saying it allows for overloading, as there are limits to be respected on the rims and the axles, etc. But they will provide for a margin of safety. At a minimum, you should not go with a tire that has a lower rating than the stock rating of 3640lbs; if you had a 2500 I would say it might depend on your load requirements. But, as you've stated a 3500, I assume you may at times want to load her up heavy, so make sure the tires will be up for the job.
- you mention that snow is an issue. So, look for the M&S (snowpeak) symbol. Tires with the M&S rating typically perform a lot better in the white and wet stuff.
The Falkens meet the above weight and M&S ratings; the Toyo AT3's also do (they were unobtanium when I bought last year). I "think" the Nitto Grapplers have the M&S also, but I'd recommend you check both the above specs on whatever tire you decide on.
BTW, in terms of "aggressiveness", I would say the Falkens are the least aggressive looking, then the Toyo's, then the Grapplers. I wanted a bit more of a subdued look, so I like the Falkens. Others may want something more aggressive looking.
hth!
Brad