Do I need a WD hitch

I would weigh the TT and find out for sure. That small of a TT won't need much. If your numbers are right and it weighs 3800 loaded and your TW is around 10% or so at 380 then I wouldn't get a WD for it. 21' isn't very long. I towed a 22' TT at 4050 loaded with a 145" wb F150 and never had an issue. When your TV out weighs your TT by almost dbl then the TV will be in control. I would upgrade my trucks reciever before I would mess with a WD hitch for 380-500lbs on a 2500. But your reciever should be good for 500lbs w/o WD. But scale weights will be the determining factor.