02 sensor replacement help??

Why fix it if there's nothing wrong? From what I have read in many articles say that the the O2 sensor after the headers. (One of two) can start functioning poorly before it gets bad enough to throw a code. And that's the only one of the two that affects gas mileage.. That's why I would consider replacing just that one sensor to rule it out. But as stated allready a few times I'm not planning on doing that anymore or atleast at this time.

 

So I took out my MAF sensor and cleaned it. It was super easy to do and took about 4 minutes not including letting the cleaner dry. It seemed pretty dirty to me. On the intake side it was much dirtier then the engine side. After re install I drove the truck a bit and it really felt better to me like it had a little more hp but that could easily just have beeny imagination. Here's a couple pics from both sides.

 

Not sure why it posted the pics twice but you can see by looking at the clean side just how dirty the other side was by comparison. I'll post results after my next tank or two regarding any mileage affect.