New 5th wheel doesn't tow well

I have been fighting the OPs description of "chucking" for the past year or so. I have switched to an Andersen rail mount hitch, a MorRyde rubber pin box, added shocks and rubber equalizers on the trailer, Bilstein 5100s shocks (all around)and Airlift air bags on my '11 F250 SRW PSD. All of these items have improved the ride in one way or another but have not been able to get the "chucking" to a level that is acceptable. I have also tried adding pin weight as well as subtracting pin weight (by adding weight to the rear of the 5th). I am starting to run out of ideas but I don't think "chucking" will likely be reduced to an acceptable level by a single change unless it is caused by a very light pin weight that is corrected.