Might want to clarify the 5th wheel numbers. You said the GVWR of the trailer 8400lbs. But say you will load it to 11,000lbs. You must must mean the dry weight of the 5th wheel is 8400. I can't image how much stuff you could add to increase it to 11,000lbs. That's 2600lbs of stuff!!!
I would say a more conservative number would be 10,000lbs loaded with a pin weight of around 2200-2500lbs. These numbers should be no problem for your truck. You need to look at the tire/load capacity label on your door post to confirm the amount of weight your truck can "carry". Try and stay within that but do stay within your max tire capacity.
S
