OP here again.
I did a bit of math and if I cough up for some 18" rims I could put on Michelin LT285/65/R18E that are rated at 3640 lbs at 80 psi. The circumference on those is almost exactly the same as the stock 17 tires so I wouldn't have to adjust anything else and could keep my existing 17's for winter. I've never been happy with the stock rims anyway. Also I got some great info from the RAM Bodybuilder site which gives all of the specs on front base weight (4428) and rear base weight (2727), so I think the upgrade to the 18" rims and tires and we should be good up to about a 4000 lb TC.
You can really go down the rabbit hole with this stuff!