2007 Chevy Impala 3.6L overheating

Sounds like blown headgaskets. You can get a DIY kit from a parts store or have a shop do the tests.

Is it while driving or sitting still? Do your cooling fans come on when it gets hot? Are you sure you got all the air out of the cooling system? Are you going by your temperature gauge or is it boiling over.?

You should have come here first , What have we learned ?

At that point, you just need to proceed with further diagnostic just as a mechanic would do. Purge the system of any remaining air. Turn on the AC as this will by default turn on all the fans. Check spark plugs for fouling due to coolant in the cylinders. Etc, etc, etc..... If you don't have the skills to do all this, have a mechanic review the car before you cause further damage.