what am I missing

What codes do you have? You can get any major autoparts store to scan your codes for free. That will help narrow down the possibilities. If the K&N filter was over-oiled, it may have coated the mass airflow sensor, causing it to read the wrong values.

Also, make sure the wires for the mass airflow sensor are plugged in properly and check for any leaks in the vacuum lines leading to the brake booster. Sometimes those can get cut or disconnected and cause the engine to run rough.

Sounds like you have failed to maintain the car properly being as it had to break down for you to change the plugs. And there is no lifetime air filter. They must be changed, or at least cleaned. Sounds like Dorian has already given you good advice. Follow a car maintenance schedule for fewer problems, and best of luck.

First mistake, well maybe not the first, was clearing the codes. Those codes don't influence performance, they are a record of what is going on with your car. Drive it for a bit to establish some new codes and then have them read to see what is going on with your car. That and everything that Dorian and Astre said.