Alright, my truck has a 87/89 dual tuned PCM from Allen in it... Normally, I fill up with regularole 87 octane gas, but on my last fill up I decided to get crazy and use 89. Well, after I filled up with 87 tonight, I checked my MPG, and it went up 2 MPG while it had the 89 octane in it! Is that normal, or just a coincidence?