Thanks 96_4wdr, for the tip. I used a replacement K&N on our prior Expy for a while. I never had an oil analysis done but did have a nagging uneasiness about filtration. I didn't like the cheap foam seal with sticky tape holding it on either. I had to be careful getting it in just right. Eventually I went back to stock for those reasons. I'm still not thrilled about factory airboxes though. I like the definite seal of hose clamp style filters, but not so much that I need to get one (with either paper or gauze). I pretty much figured that stock airflow is plenty for a truck that hasn't been modded for buku's of hp. I didn't realize it was 3X though.
Same goes for exhaust. On my powerstroke the stock piping is plenty big. It was the muffler that was the weak link. No reason I have seen for me to think differently for the Explorer.
Jam66, you started this thread trying to improve mpg's. I see you are also looking to get bigger tires. That won't help. Realize there is a trade-off and if you do multiple things at once you won't know which changes have what effect. Not bashing you, bigger tires would look good.