Welcome Longhorn! Like Worm Drowner said, there is no such thing as a dumb question here. We're all here to learn and enjoy the company of others who've PSD, or diesels in general.
If you have questions feel free to create a new thread - it'll get more attention that way, instead of being buried in an older thread. BUT you didn't do anything wrong by asking in this one.
As far as the K&N goes, I'll have to let someone who has one answer that but I'm looking into similar things myself. That mileage you got seems about right at 78 mph - that's probably about what I get at roughly the same speed.
Oh and glad you're not a Longhorn! Sorry Worm Drowner but your Horns are going to SLAUGHTER my Aggies here in a few weeks. :p