93 3.3 Grand Caravan

Here's a new problem: Again an intermittent problem. I'll be driving down
the road and the speedometer goes to zero and than back up and the trans.
goes back into gear. I originally thought it was a trans problem, but I
have an old cell phone that is powered up by the ignition key that is still
in the car. When it powers up, it beeps. And every time this has happened
the phone would beep. Didn't really connect the two until recently. I
don't have a trans problem, I think I loose power for a very short time and
that's what shuts everything down and then restarts it. It happens very
rarely, and I haven't noticed anything that might cause it, like going over
a bump. (thought it might be a loose wire). There are no codes generated.

any ideas,
thanks,
nick