OK, Trailer Life's tow rating tables give 14,200 lbs as the rating for the 2006 short wheel base crew cab 2500 with a 6.6 TD, with a 3.73 rear end and 4wd. Since that assumes only a driver and fluids in the truck, we like to discount that 10% to allow for passengers, cab baggage, weight of the hitch assembly, etc., bringing the truck's rating to 12,780 lbs.
That is entirely too light for a trailer with a GVWR of 14,300 lbs. The fact that you might not always tow the golf cart is immaterial. It is the heaviest weight that you would carry that counts.
With a 5th wheel trailer, the rear gross axle weight rating (GAWR) of the truck is also critical. Fivers, and especially toy haulers, are built so that 20%+ of the trailer weight bears on the hitch pin and thus directly on the rear axle. 2500 series trucks are going to have problems there with big fivers. What you really want to haul that trailer is a GMC 3500 with duai rear wheels.
Go lighter or get a new truck.