94 lebaron Le

I have a 94 Lebaron LE 4 door 3.0/V6. In the past two weeks the insturment cluster has been acting up. The Temp gage goes from cold to the 1/4 mark then back to cold....sometimes. New thermostat and sensor. Same problem. The gas gage goes to empty with a full tank. The Voltage gage read lower than it normally reads. This all started with the check engine light going on and the voltage going down while on a trip. Removed and replaced the "BOSH" alt. Had the system checked. The output. 14.2 volts and the amps output good too. The company had the equipment to load the system. The battery is new and all the connections are clean. Everything else seems to work ok. With AC, high beams and radio on the voltage drops very little on the gage and doesn't seem to affect anything. Haven't had a chance to have the codes checked yet.
Took the car to the dealer. All test were good. No problem found. I also have taken it to several other test centers and same results... no problem found. Yet the car on a long drive, acts up.

maybee the body control module got messed up when the alternator died