anyone seen there speedometer,gas needle or hesdlights flicker???this happens when only driving down the highway.any ides?

I haven't had this happen on my Astro yet, but something similar happened on my Jeep (and my cavalier too, come to think of it). In my case, it turned out to be a loose battery terminal connection on one, and a really corroded connection on the other.
On my Jeep the head lights flickered, the gages went wacked, all in perfect time with every road vibration.