OK, so last week my truck was throwing these codes. I looked over all the vac lines, and everything was fine. Had the MAF tested and it was junk and causing my truck to stumble in the midrange. I cleared the codes and they stayed off. Now I replaced the MAF with a brand new stocker and added a CAI. The codes just keep coming back. All the hoses and lines on the intake are super tight and the MAF is perfectly fine. The only other thing I can think of is maybe its time to change the fuel filter? My truck has no rear cats, could the oxygen sensors finally have realized that they are missing (rears have been out for 4 months and a SES light never came on). As far as performance goes, everything seems normal. What are my possible problems before I wind up throwing money at shit I don't need?