What is causing my check engine light to flash. I have had the plugs, ignition coil and valve cover gasket replaced.

If the check engine light is flashing it indicates there is a miss fire of one or more cylinders. When the miss fire occurs raw fuel is dumped into the exhaust. This fuel will burn at the catalytic converter overheating and possibly melting the inside of it. Do NOT drive a vehicle with a flashing check engine light or you may do damage to the converters. Sounds like you need to get the trouble code read and do some more diagnosis.

Thank you sir!!!

For a good explanation of flashing check engine light go to the link.....http://blog.carmd.com/flashingcheckenginelight/

When i start my trailblazer yesterday the engine light come on but when I go the speed limit 45 to 50 it flashing then I slow down it stop