I would stick with the Voltage or the Impact. The 18k tri axle trailer are safer to stop and with 6 brakes are hands down superior to tandem axle braking. However 16k-18k can push the back of a non DRW truck around which can be dangerous especially on wet pavement on a twisty downhill grade.
Actually the 13350 lb tow rating and 21000 GCWR with a 3.73 gear ratio is for a GN or 5th wheel trailer. If the truck has the 4.10 gears then the tow rating increases to 16800 lbs and a 24000 lb GCWR.
Dodge for some odd reason issued a very low 10xxx GVWR and a 6500 lb RAWR on the pre '13 model 3500 SRW trucks. For '13 they pumped them up to 12400 GVWR depending on truck configuration with a 7000 RAWR.
Your tires, and hopefully the wheels, were uprated to 3900 lbs . All thats left is rear suspension help if it needs anything at all which I doubt. I wouldn't do a thing to the truck till its loaded and make short trip. Then is the time to decide.
Dodge rates all '11 3500 SRW with a 6500 RAWR. Many owners report rear axle weights in the 2800-2900 lbs range when empty which leaves around 3500-3600 lbs for a payload.
Its not necessary you pull a TT unless you just want one.
