With each upgrade I've done (Tune, then DP's, then FMIC & CP, then Aplina A6 flash) I've found that if anything, my fuel consumption has improved..
My driving style hasn't changed, so assuming everything is more free flowing - and thus not working as hard, you'd expect better fuel economy - no? Highway trips are pushing 800k's per tank!
Granted that it has a bucket load more power, so if I get on it - well - lets not go there.
Rear mufflers are next on my list and although I love the PE - I like to be a little different too.. Stay tuned! BUT I think kaitan is on the money - New exhaust brings a heavier right foot just to hear it!