Xposure

My car is mostly stock except for a Granatelli Fuel pump, K&n CAI, and Flowmasters. It developed a weird fuel issue over some time. Everytime I go fill up I can only put upto 10 gallons. I know that the tank can hold 14 gallons easy so im wondering what could cause it stop it at 10 everytime. I have tried goin to 11 gallons but it will start overflowing. Every time i fill up it does seem to act empty at around the same place on the gauge so im pretty sure its almost empty everytime.