1998 Suburban pinging

[98BLACKBURB]

I have changed O-2 sensors,fuel filter,air filter,tryed Seafoam in gas tank,and top-end,all of a sudden it likes 93 octane instead of 87 which never give me trouble before, I believe it is ignition related now, it has a 350 w/146,000 miles ,was tuned up w/platinum plugs and cap and rotor by Chevy at 90,000.is it time for a tuneup or do I need something else?EGR? Can you help me?

[GM-Tech]

carbon buildup, wrong heat range plugs, etc.

[98BLACKBURB]

carbon buildup, wrong heat range plugs, etc.

 

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timing,injectors,spark advance,etc.