Instrument Cluster Issue

I'm trying to troubleshoot a mystery. My 2000 Gen 3 Sport is due for registration and the shop can't get the "Check Engine" light to stay off. After all the usual fixes (plugs, wires, emission testing etc) they are convinced it is an instrument cluster problem. But strange things are occurring. While driving at a moderate speed if the high beams are engaged, the transmission appears to shift from Drive to Low--not just the indicator--RPMs go from 3000 to 5000 RPM. If idling in Drive with the foot on the brake and again engage high beams, the gear indicator goes from Drive to Reverse, the the transmission remains in Drive.
My shop mechanics are stumped. Their research indicates it is not a completely unheard of problem and it is the Instrument Cluster.
Anyone heard of such a problem? Can a bad Instrument Cluster affect the transmission? Any thoughts?

 

Has this car been in a flood? With so many things happening, I am baffled as to what it could be. I don't think instrument cluster is to blame. Perhaps the ECM but then this is just a conjecture on my part. Does the OBD throw any codes?

 

Make sure the mechanics have checked ALL grounds POWER connections to the ECU.

Can the car run without an instrument cluster? If so, I'd disconnect and see?

Try a different cluster from a junkyard?

I have heard of the instrument cluster doing odd things but not to this level of craziness.

 

Never been in a flood. I'm hearing different things from different sources. One company that specializes in instrument cluster repairs states that it does happen and they have repaired such problems. Another says no way. "I've been doing this work for 30 years and never seen such a thing" said one. I don't know who to believe. Does the one just want my business? Thirty years for the other. That puts him long before the current cluster equipment and technology was around. My inclination is to send the core out to the company that claims they have seen such problems but I sure don't feel confident about it. I'm going to try to have my local mechanic talk to the instrument cluster guy. See if he gets a clear read from them. . .