Do you have an engine lope at idle or surging while driving? Are you seeing unusual rail pressure fluctuations? Your LB7 Inlet Metering Valve may be the root cause. 

 

Also known as the FCA (fuel control actuator) or the MPROP, this component can wear from age or poor fuel quality causing inconsistent travel in the spool valve. The MPROP controls the flow of fuel to the CP3 pump. A crucial part of the high pressure fuel system and if not functioning properly can cause severe running issues.