I know you've talked with the folks at Gafney, but have you talked with their free helpdesk?
I would talk to the Help Desk (have your vin number handy), to determine what instrument system you have. The help desk is 1 800 FTL-HELP. The help desk has always been very helpful for me.
From chassis year 1999 to sometime in 2004 was their System III instrument system, which had a vehicle data computer collecting all the data and sending it down the data bus to the "message center" (lots of lights/symbols). From the message center, a spider harness sends all data to all instruments and the instruments get what they need.
The next version was MMDC, used from late 2004 to 2006. I do not know exactly how it works. After 2006, a different system was used.
My point is that not every wrench turner will know what to do to find your problem.
After getting the instrument system identification info, I'd ask them to send the troubleshooting documentation to you. You would at least have this to provide to the person attempting the troubleshooting.
On the instruments, I think you have a bad or corroded connector somewhere in the system. On the System III, I'd be checking the connectors on the VDC, any connectors between the VDC and the message center, and the connector from the message center to the gauges.
If yours is the System III wiring, you can get the technical info/troubleshooting steps from this web site.
copy of freightliner service bulletin 54-12I hope this info helps you. Good luck.
Fred
Fred & Vicki
St. Augustine, Florida