2006 GMC envoy
My check engine light came on flashing
truck running really hard
Pull the code(s) and read them to see what could be the problem.
Mary, you shouldn't drive it when it's flashing. More than likely one of your 6 (assuming you have the common I6 engine) coils has failed. Bring it to an automotive store and have them read the codes for you. You should see a P0300 or P0301 thru P0306 which should pinpoint which coil it is IF indeed it's not a P0300 which is multiple cylinder misfire.