a friend called me last week. his 03 started running bad, then wouldn't run at all. I went to look at it, smarty had codes for low and high fuel psi. my other scantool had same codes but said rail voltage high and low. I checked fuel psi @ cp3=3psi at idle. started it, idled rough, brought it up to 1700 rpm and the quad rail pressure gauge spiket to 30,000 and died. checked codes again -rail psi voltage high. told him it was probably rail psi sensor. he replaced it, and still has same symptoms. the truck had a smarty, quad std, and tst on it before it cratered, everything was taken off before testing it(put quad back on to monitor rail psi)