Why did you buy a 3500? Maybe not necessary in your circumstance... the 2500 would have been a nicer-riding truck.
One word Payload. 2500 limited mega cab diesel with sunroof and ram boxes would have been about 1700-1800 lbs. Add 4 guys to the truck, all our gear, and trailer tongue weight and we are right at the "legal" payload capacity. Heck, my current truck has around 3800 lbs. payload I believe and has 2300 more GVWR (12,300 vs 10,000).