2005 Chrysler PT Cruiser shakes hard at about 20MPG, slighl

This is a drive line issue. The following need to be checked:

The front wheels (Balance & out of round/bent), wheel hubs, ball joints, CV joints and axle shafts.

Don't continue to drive your vehicle with this condition. It will certainly make your problems worse. And I've seen entire wheels pop off on people while cruising down the highway. Not only can this kill you, but other people as well.

BE CAREFUL!