Hey everyone, I do the work on my buddies car and there is an odd problem I haven't heard of before. Every time he fills up on gas his speedometer and tachometer go screwy until he burns through about 1/8 of the tank maybe even a little less than that. What happens is that the speedometer won't go over about 20 mph and the tachometer will shoot up to 6,000-7000 rpms when it is really around 2,000 rpms. He says this hasn't happened under any other circumstances other than when he fills it up. Could this be a faulty cluster? Thanks for any input.

Car has about 105,000 original miles, has had no major issues or work, and is not throwing any kind of codes.