White smoke on startup and dnostic showing #1 cylinder misfire

[Bigoledude]

My 2007 Armada started blowing white smoke on starts. Then, it started to run rough. If I'm running down the highway around 50mph and try to accelerate, it really starts to run even rougher. Even while at idle you can feel a definite miss.

The first diagnostic check showed #1 cylinder misfire so, I bought a coil. After installing the coil and allowing 20 minutes to reset the computer as directed by auto parts store clerk, it hasn't improved 1 bit!

[marctronixx]

valve cover gasket worn possibly...

[Headwi]

Over two years, had to replace two cats due to this white smoke problem clogging them. Went to two independent mechanics and dealership 3 times. Dealer said engine was shot and gave me prices for new and used. Saw on a forum others with same problem. Changed $130 plastic valve covers and gaskets. Been running like new ever since. 4 years ago