Ping monster has showed his ugly head!

[DZEE'S LX]

A couple weeks ago I noticed pinging. Thought it might be bad gas but a new tank now hasn't fixed it.
It has been hotter 90 - 100 deg but my car has never pinged during the summer for the last six years. Even after all my engine mods it has always been "pingless".
It is doing something else strange now. At full throttle and about 4500 rpm the engine suddenly pulls harder like an abrupt turbo boost, but at that same time the pinging starts and goes nuts. If I roll into the throttle gradually to wide open it doesn't seem to ping much.
It's almost like the timing jumps at 4500 which gives me more power but obviously is too much for the mid grade and 18 deg timing that I have always run.
Bumped the timing back to 15 and the pinging is still there at top end but the power surge at 4500 is not noticable now.

Is my distibutor the problem? What actually advances the timing as rpm increases. Still using the stock distributor.

I would blame it on hot weather and too much timing but it doesn't make sense that it has never done this BS before.

Please help this be a cheap fix!

Dan