So, FWIW, I tow a 4300 lb boat and trailer all the time w/ My Air Ride+Mag Ride Denali, and it is smooth. As a matter of fact, I almsot think the ride is better w/ the trailer than without. Just towed this thing 1000 miles round trip, and one of my passengers commented, on about mile 700 "This Vehicle has to be the smoothest riding I have ever been in."
First, you should always have the trailer tongue level w/ the road, so you probably should adjust your drop.
Second, there is a TSB out for a kinked/pinced air compressor intake hose...I would check this hose to make sure you don't have a restriction, but would think this would flag a DTC in the system.
Third, you need to load it so you have about 10% of total weight on the tongue...best way to measure this is on a scale (See if there is a CAT scale near you, and measure it). If I had to harken a guess, you are getting shook because the tongue is pulling on the rear end...likely not enough tongue weight, although I would expect you to feel this in any tow vehicle...
Are you sure the load in the trailer is centered left to right? Perhaps the anti sway is kicking in due to this?
Definitely ponderous...but, my towing experience w/ my boat is fantastic w/ this rig.