Any ideas on an intermittent fuel gauge on a 2010 XFR?

 

XFR, I would venture to guess that your float inside of the tank is making intermittent contact and therefore making the circuitry think the tank is going from some level to empty and back. I had a level gauge do this to me and it was one of the wires on the float that had broken and was periodically touching. I would say to first put the instrument cluster into "Engineering Mode" and see if the indication there matches what is being displayed on the dash. If the data matches, then your problem lies between the ECM and the fuel tank. If it doesn't match, then you are looking at a problem in the dash somewhere.