Lose electric when hitting a bump

I have a 94 chevy 1 ton work van. Recently I hit a bump in the road and lost all electric and the engine died. I managed to get it started. This happened twice after that when hitting bumps. It ran fine for a few days but now if I hit a bump I lose all electric and my transmission gives out, the van will stay running now but everything else goes out! Any ideas? Sure wish I could avoid every bump in the road! LOL!