Help?!?’! MPG is done so??? What am I missing!?

So I recently changed my wheel bearing because it was rubbing against my wheels and forced my car to run it about 35 to 37 MPG. However, I managed to get those fixed and for about a day or two it went back up to 43 mph, but A week afterwards, after getting all the repairs done and changing out the spark plugs, pvc valve, and cleaned out all the throttle and replacing the airflow sensor, I’m back down 37 mpg!! Can someone tell me what I’m missing because I literally upgraded nearly every part including an K&N air filter about two or three months ago as well, and even had a mechanic clean all those the cleaned out the whole intake manifold on the same day as the spark plugs when in. Im gonna to put in my 44k tomorrow as well as soon i get them in the mail. No one is really been able to figure it Including the cleaning. I am also going to change the ignition coil and Thinking about ordering a brand new O2 sensors as well. Does anyone have any suggestions or solutions to this problem?