Our roads in the US are in such poor shape that this effect is often the result. The right lane is the one the trucks use and it gets beat up by the weight. Moving to the left when you don't obstruct traffic is one way to compensate. When we drove our DP I would increase the air bag pressure the ride was a little stiff but it ended the porpoising. The other thing to consider is if you are using a WD hitch you may have shifted too much weight to the front. You may try dropping 1 link and then see if the ride improves without making the front feel light. Good luck on these roads. I came through Wisconsin a few years back and I thought I was going to shake myself to death.
