Jim:
Inflate your rear tires to the maximum specified sidewall pressure before anything else. Thhe stiffer the sidewalls are, the less 'tock and sway' you'll feel.
With my pop up, i'm under the cargo capacity but I run the rears at maximum specified (on the sidewall) pressure all the time. In my case 80 psi cold.
Always run wider than stock tires, since way back when. I had to add spacers so at full lock, the tires wouldn't rub.
Never really had an issue with the Lance either. The sway or rock or whatever you want to call it was more than the Palomino, which has none but it was never a cause for alarm, was just there and I adapted to it and the Lance was a sky scraper compared to the Palomino.
