Engine noise

2000 ford f150 4.2 L v6
I was driving on the interstate at 70 mph - the
service engine soon light has been on for a month or so (I have a manifold gasket leak, assumed it was just that). Light began to blink and I stopped to let vehicle rest and added a quart of oil (rear main seal has a slow leak). Returned to interstate, and truck engine will ping whenever I accelerate while driving uphill at speeds over 70 mph. Is this a misfire issue, do I need new spark plugs, is my engine about to blow and need to be rebuilt? 218,000 miles and counting. This is my only transportation, cannot afford a new truck, and it has sentimental value.
I guess I would've loved my horse too if this was 1910. Thanks for your help.