I used to use fram on my 2 5th gens. then when i got my 6g i switched to a K&N, after doing some research and talking around i learned that the K&N filters are designed for the racing end of the spectrum, good filters but designed more for higher flow than filtration. so i switched to a mobil1 filter since i use mobil1 full synthetic oil. figured might as well match it up. once i started school we got into a heated discussion about filters in my engines class, my instructor (an ASE, mitzubishi, Nissan, and Honda master tech/ subaru, chevy Senior Tech) brought out cutaway's of different filters and compared them to personal encounters with cars he'd worked on. Fram being the worst filter, then Motorcraft, K&N (this class was viewed from the DD/reliability point of view), acDelco, Puralator (he used that because of price for efficiency), then OEM being the best. i asked him about mobil1 filters and he admitted to having little experience with them, but he never heard anything bad about them in the 30some years hes been in the auto-tech industry. so i stick to it. hope some of this was useful to you, and/or anyone else reading this.