Put some X chocks in between both sets of tires, this will stop forms and aft motion from the tires. Make sure rear stabilers are down and tight. We use wood blocks under ours to spread out the weight. We also put 4x4 under front jacks to keep legs as short as possible. Doing v this has take out most of the shake.
I've don't have JT Strongarms but I hear they work great.
In order to stop most if not all shimming you need to get the weight off of the axles. Put a jack under frame fore and aft of axles and that would help. Only other option is six point leveling which our new unit we are a out to order will have. I'm just too tired of dealing with all the above and having to level the unit. Good luck and enjoy your new fiver. Happy camping.