Start the car up and it feels like my '02 Z28. You can barely feel or hear it but I take notice of these things. These things idle like sewing machines so hence my concern. I think there is a drop in midrange performance. Gas mileage is slightly suffering. Was going to check the plugs till I found out it didn't have any. Unless I am wrong? I run 93 octane all the time. Through in Berryman fuel cleaner. No change. Oil looks good but goes as fast as the gas when your liberal with the peddle. Think the valve cover is leaking in the back but not wet and nothing on the floor. Possibly rings. Makes as much motor noise as an LS1 so not bad at all. Have not noticed and codes that would suggest anything wrong. Next step is pressurized fuel service. Any other ideas to what could cause this?