I have bought a Fass 165 Titanium Signature series pump that came off a duramax. Bought the correct fittings to hook it up to my truck and also installed a sump. Pump flows good into a bucket, getting good fuel flow without air and such. But when I hooked up a electronic pressure gauge through my Edge CTS2 it shows only 8 PSI at idle. My question is can I adjust the fuel pressure by getting just a new spring for the return line to increase pressure? Or is there a new assembly I should be buying?