I could write a book about pinging in this engine. Mine has pinged for several reasons.
I would start by cleaning your MAF. Search on this website for instructions. That will probably get rid of some of the pinging.
Run a can of seafoam into the intake manifold per the instructions on the can. This will decarbonize the engine and help the pinging as well.
Also, make sure your oil level is not up past the full mark on the dipstick. Occasionally they get overfilled by a shop in a hurry. If you are overfilled, the engine will pull oil thru the pcv valve causing heavy pinging.
Does your 5.0 use oil between oil changes? If so, it may be pulling oil thru the pcv valve. Had that on mine. I have problems with 5w and 10w oils, which might be what you are using that far north. A 15w 50w seems to help quite a bit.
You can have the dealer check and make sure that all your sensors are ok ( MAF, coolant temp, etc.) and have them update the PCM software as well.
In general, if the dealer checks out the engine and finds no issues, and you have heavy pinging under load, oil coming thru the pcv valve is very likely going to be an issue.