I'd thoroughly research the amount of truck payload you'd have left over on an empty 13,000 lb 5er. At 15% pin weight, you're at 1950 lbs. At 20% pin weight, you're at 2600 lbs. With the 2500 and 3500 SRW, you're limited to 3.42 gearing. With the 3500 DRW, you can opt for the 3.73's or 4.10's. If you tow a lot in mountainous areas a large percentage of the time, the overall towing experience would be more pleasant in a DRW. Spend a little time here http://www.ramtrucks.com/en/towing_guide/tow_chart/2500 will work fine for me.
I'd thoroughly research the amount of truck payload you'd have left over on an empty 13,000 lb 5er. At 15% pin weight, you're at 1950 lbs. At 20% pin weight, you're at 2600 lbs. With the 2500 and 3500 SRW, you're limited to 3.42 gearing. With the 3500 DRW, you can opt for the 3.73's or 4.10's. If you tow a lot in mountainous areas a large percentage of the time, the overall towing experience would be more pleasant in a DRW. Spend a little time here http://www.ramtrucks.com/en/towing_guide/tow_chart/