If it IS an octane issue, I like this stuff: http://www.maxlead2000.com/ The site seems to be way cheaper than the retail vendors I've seen (like at Carlisle.)
I also like STP's Octane booster. It takes the edge off and I can get it at Ft. Belvoir for $1.99, yes 2 bux. At Advance Auto it's $4.50+