Im fighting lower fuel pressure on a 07.5 6.7. The rail pressure drops off after 2000 rpm on a stock tune. The turcks history is unknown for sure. The used car lot said that it had "upgraded injectors" and that the fuel filter had been changed. On my inspection i found that the fca is new and a rail plug was installed. Retorquing the rail plug help a little. So it was replace with a new releaf valve that i shimed with no change in top end fuel pressure. Any insight would be great thanks.