My 2012 F350 SRW LB is most often fine, but on some stretches, for example I35 coming out of Minnesota into Iowa and then on the Iowa stretch, it porpoises so badly you would swear the front end is going to lift off the ground.
I am within all the numbers in terms of weight and it made no difference whether it was our Hallmark popup or our Northstar Laredo. Ranchos help, Super Springs made no difference at all. Also had it happen on a very short stretch crossing into PA. from New York. When it happens, it is instantaneous. The previous owner opted for plow springs on the front end, which is ridulous overkill considering what we have in the bed and I wonder how much that comes into play.
Again, just another work in progress.