I have some guesses.
You have oiled your filter and now that oil has gotten on your MAF sensor. That can gunk it up, attract dirt, and affect performance of the sensor. Make sure your filter is not over oiled, or wet, and getting oil (or water or anything else) sucked upstream. Also clean your MAF again with brake cleaner and make sure it is COMPLETELY dry before reinstalling. And do this after you have verified your filter is not oiling/watering your intake air.
Also, check downstream of the MAF for ANY kind of air leaks in your intake. But I have a strong suspicion this is something to do with cleaning that filter.
2005 Mustang GT with 300 ci 04 Cobra iron block, Kenne Bell 2.6l twin screw, P&P S3 Heads, SS valves, Comp S3 cams, Currie 9+ 9" rear end and DS, Hurst shifter, BMR K-member, A-arms, LCAs & UCA, JBA long tubes & mid-pipe, Accel COPs, Dual GT500 fuel pumps, much more...
670 RWHP, 640Tq @ 16 psi & 6400 RPM