I have the 3815 superchips flashpaq. 5.9L. I have it programmed to the 91 performance tune right now with a tank full of 93 octane gas. I want to program it to the mileage xs tune but idk if it is going to mess anything up being that it is running 93 octane. Can/should i run 89 with the mileage tune or should i stick to 87? I was just going to wait until i got to around 1/4 tank and fill up with 87 and then re-flash it.