2002 F53 chassis

I've got a 2003 29' Motor home on a Ford f53 chassis with the V-10 engine. I'm finding it to be very unstable at times. It shakes but not enough cause concern. But it does seem to shake. I've had it aligned and tires balanced and recently had the Ford truck dealer try to find the problem. They "tightened the ball joins" and said it "rode like a Cadillac". Not quite. The next trip I hit a certain frequency of bumps that almost shook the unit apart. I had to slow down to 10mph (on a highway) to stop the violent shimmy. The RV newsgroup suggested a couple of after market stabilizers. but I'd really like to explore Ford specific info first. Does anyone have any info on the fix for 2002 F52 chassis shimmy? Could the rear end cause a shimmy? Thanks in advance, Tim fm CT