Thanks all.
I currently have x-chocks on both sides, and I use the Andersen levellers. Not enough.
I'm gonna need something more. I've heard good things about these, and the cost seems reasonable.
http://www.campingworld.ca/shopping/item/universal-rv-stabilizer/34337
I'll put one under the back bumper, where the sway is coming from, and one along the side close to the wheels. That should help, if they performed as advertised.
My other thought was to add scissor jacks just ahead of the wheels, if the x-chocks aren't solid enough.
Thoughts?