Hi all: I've an '05 GT, 5 speed, runs great in the worst LA traffic in the world. It's high mileage, at 150.000, it pings lightly under light to hard acceleration. I'm running 89 octane, up from the 87 stock spec. Is it valve/piston top gunk? Tuning? Should I run 91? I can't tolerate pinging, even at a small scale. Please Advise. Thanks, all, Jason.