Pt cruiser limp mode

Where should I begin to look for the cause?

This is really strange , my car shifts gears fine until I hit a good bump along the street. Once it hits a couple manhole covers or potholes the dash display flickers once or twice and the transmission stops shifting past second gear. I do not believe this is a mechanical problem because it always seems to happen when there's a few bumps or potholes? Has anyone had this problem and how did you find the issue? Where should I look,it strikes me as an electrical problem?