I have a 2006 5.3l that I put a new rebuilt engine in due to very high mileage and bad camshaft. afrer re-install engine has misfire on cylinder #5, (according to Chevy house, they performed compression test and all cylinders seem ok, they changed coil packs (interchange with other cylinders) and still is on number 5 any ideas? Truck idles rough and will barely get up to around 45 mph