I had a similar situation when I traded in my '01 Expedition for my '11 F-150. Dealer said when empty, leave 2 links on my leveling hitch, but leave 3 (more weight transferred forward, because of more load on the chains and bars) when the trailer got loaded. I used 3 for a couple of trips and bounced a lot. On the way back from my last trip, I switched back to 2 and it solved the baoncing and jarring. I guess I just don't run as loaded down as some... With the 1-ton van, your problem will probably be more difficult to solve.
J & D in Lovely Weatherford, TX
2016 Jayco White Hawk 28DSBH TT
2014 Ram 2500 Crew Cab 4X4 6.7L Cummins