If you want to order a truck, then I agree skip the 2500 and get the 3500. The price difference is small. If, however, you are buying off a dealer lot, the 2500 properly equipped is fine. Around my area you seldom see a 3500 SRW on a dealers lot. The rear axle weight capacity difference between many 2500 and 3500 trucks is minimal. My 2016 Ram 2500 has a RAWR of 6,500 lbs and you get 500 more lbs in a 3500. As you start approaching 14K you may need the extra 500 lbs, but the weights you are talking about is WAY below that. I got 11 mpg pulling my 12,500 lb loaded fiver with my former 2015 Ram 2500 with Cummins diesel (which was destroyed by flood sitting in my garage). My current 2016 Ram 2500 with the 6.4 hemi and 4.10 rear gets 8 mpg pulling the same 5th wheel. Good luck.