Scroll down ,you`ll see my other post with a complete list.
Engine temp, engine timing, fuel , octane rating,spark plug heat range can
contribute to "dieseling at shutdown"
changeing the heat range of the plug is the very last thing you want to do. 90% of dieseling is to high an idle rpm. 9.9% is everything else on the list. That last .1% is the plugs.
Have you checked through the adults only section yet?