Your pinging may be from carbon buildup on the tops of the pistons and other areas. The decarbon method you used may not have been adequate. There is a cleaner from motorcraft that is sucked in through the pcv hose (or any high vacuum hose) while running the engine at 2000 rpm after it is warm. Shut the engine off and let it sit for 10 minutes. Drive it hard and then repeat. Change the engine oil and filter when you're done and it'll be as clean as you can get it without taking it apart. If it still doesn't satisfy you, then you can retard the timing. Depending on the year, there is an actane adjust plug in the harness by the edis module, or it is a setting that can be changed in the computer.
