1999 Chevy Silverado engin pinging

hi, I have a chevy silverado 1999 with a 4.8ltr v8. It has started pinging about 7 months ago and it does it under a load , while im just driving 55mph on cruise control and when i rapidly accelerate. I have replaced the spark plugs , fuel module in the tank, fuel filter, air cleaner, high octane gas, cleaned fuel injectors, used sea foam to clean out the carbon . NO DIFFERANCE AT ALL ! I questioned the timeing but the dealer says that its auto adjusted ?? Scanner was hooked up and there was no prob with any sensors and the check engine light has never came on . What gives??? Something is causing the prob and i know it can be fixed. I just dont know how. I'm at the end of my rope . Can you help me ??

thanks Randall