2006 Chevy Avalanche mis fire

Engine Performance problem
2006 Chevy Avalanche V8 Four Wheel Drive Automatic

I have 2006 avalanche 2500 8.1 ltr. I recently have code P0300 random / multiplecyl. Misfire detected. That happened when I stepped hard on the accellerator, but when I release the accellerator the check engine light disappear.

In minde these message coming after I changed the tires and the new tires are bigger than the old tires

Also I changed the spark plugs. For the old sparks they were in white color and I drove it just 6216 Mil (( 10000KM ))

Thank you for your help