Dave, I highly suspect you have a problem with the VDC (vehicle data computer). The FL VDC/VDU in those years were notorious for having some cold solder joints that cause the exact problem you are having. I had same issue with my previous coach, a 2002 Journey. The fix is pretty simple if you are good with a soldering iron or pencil.
A new VDC is about $400 from FL. If you want to try and remove the VDU and do the repair yourself, send me a PM with your email address and I will send an article with pics and instructions on the repair.