As far as the mileage coming down afer intake/exhaust - that's what I noticed. Ideally those mods should increase your MPG, maybe ever so slightly but still...mine seem to have dropped but by very little.

Now the more mods I have the wrose it becomes - I still love it and at this point don't really care about mileage. There's nothing I can do about it anyways so I might as well just enjoy it.