Not aware of any problems/complaints with the 3500 air suspension. Availability of aftermarket suspension parts/upgrades are much more limited (vs. non-air). Although I don't think it's continuously adjustable, I believe it does have 2-3 presets that will vary the height somewhat.
My guess a 3500 SRW 2WD should have over 4,000 lbs. of payload in the lower trim levels. May drop below 4k with a higher trim level due to the weight of the additional options. It should handle a 3000-3500 lb. loaded camper just fine. If 3,000-3,500 is the camper's empty weight, then you're probably looking at 4,000 - 4,500 lbs. loaded.
