Spark Plug Change in a Truck--How Hard Can it Be? Update#2

You should look into an intake cleaning. Likely getting pinging due to carbon build up in hot temps/high load conditions. Try moving up to 89 or 91 octane for a tank and see if that stops the check engine light when towing up hills. If so, that tells you you have carbon build up. You also likely need plugs. I'd DIY.