truck starts fine but idles rough and seems like I've lost power

Hey guys,

I have an 04 F350 with the 6.0L. Aftermarket exhaust and a K&N filter.

Recently it seems as if it idles a little rough like it's missing or something, and I swear it's like I'm losing power. Any ideas what it could be?? I didn't change my fuel filter with the last oil change, could that be it??

thanks!