I bought this Acadia a few months ago and suddenly noticed a surging while driving. The rpms go up and down about 500 when doing it. The transmission shifts out great with no issues. Today I checked the fuel pressure before starting it and it held at 60 psi. Then when I started it, the gauge goes from 10 psi to 90 psi. There is a clicking noise that appears to cause the changes. Any help is greatly appreciated!!!