My 2003 GMC Sierra 5.3L with 161,000 of my miles, runs great, but pings loud only in process of reving on the way up towards high RPM's. This only happens with 87 Octane, as what is the standard rating to use. If I put in 92 Octane or 92 Octane with no Ethanol, it does not ping under the same conditions. What is causing that and what can be done to eliminate it? Re-program at the dealer? Something else? Thanks!