We recently bought a '13 GC w/ Hemi and looking through the manual, it actually says they recommend 91 octane or higher. I searched threads here and read that you should go no higher than 89... It's on page 124 of the manual from the Jeep website. Costco by us only sells 87 or 93 and for the first few tanks we've been putting 93 in. Anyone else care to weigh in?