2004 Ford F-150 maf sensor

My truck started running bad when I ran it low on gas and the check engine light came on. I assumed it was trash so I changed the fuel filter, put some gas treatment in the tank and filled 'er up. No help. A local parts store put a code reader thing on it and it mentioned two codes which I don't remember. But they were both relateted to the O2 sensor. The guy said it was most likely the MAF sensor. I cleaned it with electronic parts cleaner and it ran fine for awhile and then it started acting up again. I replaced it with a reconditioned MAF unit and it is still doing the same thing. Now what?