Got a 97 f150 4x4 with a 4.6 and 5 speed and 355 gears. It calls for 87 octain but it don't run good on it. Runs like a top on 89 though. Is the 87 octain really 87 with the ethanol in it? Says in my owners manual not to run 86. Will 89 be ok to keep running in it?