When passing slower moving vehicles on two lane roads or up hills my 94 XLT with 170K miles begins to ping above 70 mph until I lift my foot. I have done the following with no permanent fix: Replace fuel pressure regulator; replace ignition wires; replaced upper intake manifold gaskets;change to platinum plugs; used mid grade gas; cleaned the MAF twice a year; replaced oxygen sensors; and installed K&N air filter.
If anyone has had similar symptoms and found a permanent fix I would love to hear about it.