Did you get the right plugs or the ones the counterman said to get? AC/Delco 41-103.

What is the coolant temp doing? You are sort of describing overheating.

 

The plugs are platinum and the coolant is now under 197 but looks like I found the culprit. I knew I was hearing an exhaust leak even after replacing the CATs so I figured maybe the bolts were not tightened or maybe another gasket is needed but I found A fracture in the exhaust pipe. I put another one on and my car is back running quiet and smooth. The MPG is slowly going up so hopefully I get back to the 29-31 MPG as before.

 

Ecotec 's don't like platinum plugs they are designed and built for iridium plugs, AC Delco as Don pointed out

 

Wrong plugs! 41-103 are Iridium and will last at least 100,000 miles and the engine is built for them.

But we were wrong about the flex pipe, too.