TM lurches forward and back - why?

[Edit - this thread was de-hijacked from another.]

We just picked up our 2720 TM; our TV is a 2008 Toyota Highlander (5000 #). The dealer installed a WDH with torsion/stabilizer (?) bars to keep the TV level. Driving on city streets we experienced severe forward and backward lurching. No brake was engaged. Above 40 mph and on the freeway we did not seem to experience this problem.
Is this normal? Is there any solution to this problem?

Jerry
2008 2720
2008 Toyota Highlander