Aha, I bet the 91 octane is the culprit. I'm running 93 octane, and I got lined up at the track with a SHO that had the same mods and an E30 tune. I ran 104mph he ran 112mph. We were neck and neck till almost the 1/8th mile. On the big end though, he absolutely walked away from me. So from my limited experience, I think higher octane lets you tune to be much faster.