Hey, I have a 2000 GMC Sierra 5.3l V8 with 161,000 miles (260,000kms) and It has a P0300 Random Misfire code. The truck runs perfect around town and on the highway but the misfire is relative to RPM. If i hold the revs at 1900rpm or more it misfires and the SES light flashes. So on the highway at about 70mph or over it will miss. around town it does not unless i put the shifter into 2nd and let the RPMS climb. The Truck has Had a FULL Tune up. The only thing done besides a Tune up was a new fuel pump installed last year. Has anyone encouterd this issue!!?? Maybe the Intake?