Only suggestion I can make is to turn the pumps on low when next you see the fluctuations. If the fuel flow continues to fluctuate then it is the gauge - if it stabilises then where does it stabilise?
i tried this. it continues to fluctuate , with tendendcy to worsen the needle jumps. so i think we keep on going until next 100hour inspection and then tell the maintanance to look carefully at the gauge , sensor and wiring.
you have experience on a C404 in photosurvey ?