I know that a few years ago a major oil company gas station, here in the Virginia Beach area, was convicted of selling 89 octane gas as high test. They had 89 octane gas in both it's middle grade and high grade tanks.

I'm not saying that's what's been happening to you. But, who knows???

I do know that I haven't had any problems with pinging and I drive mine pretty hard.

Good Luck!!!