brianseay1, I had a similar problem on my Monaco....1/8, then 1/2. then totally out in right field!
My problem was a failing fuel sending unit AND a bad gauge.
First I called the fuel sender company and they emailed me a document to test my sender, proving my sender was bad.
I ordered a new sender and installed it, but my gauge still was not correct.
I went to an auto parts store and bought a cheap fuel gauge and borrowed a 12VDC car battery.
I opened the driver side fuel door and found the wires leading to the fuel sender attached to the diesel fuel tank.
I marked each of these wires and disconnected each and electrical taped all ends.
I then ran wires from the fuel sender to the new gauge and battery.
The battery was at my feet and the new gauge was on the fuel tank next to the fuel sender......this was basically a test bench.
I unscrewed the fuel sender from the tank and lifted the sender up out of the tank simulating less fuel in the tank.
This should show the fuel gauge moving towards empty.
The new gauge reflected this.
When I disconnected my "test bench" and returned the wire connections to the fuel sender, my gauge still did not show the value that was on the new, test gauge.
New gauge went into the dash, old gauge became a rifle target, and all is reflecting correctly now....1/8 is 1/8, 1/2 is 1/2, and full is full. I have many detailed photos of this test that I could email you....just send me a PM.
