1991 Olds Custom Cruiser(caprice)

Not sure what to do at this point. Timing and fuel pressure good, have replaced every sensor, ESC module, but still getting some pinging on 93 octane starting around 1500 rpm. The engine is a new 305 goodwrench. The old and new motor both exhibited this.

Only thing not stock is it hasn't got a cat on it. Got so clogged up it wouldn't run, so I got rid of it. Also added a heated oxygen sensor so it would warm up quicker in the winter.

Don't really know what to try next. New fuel injectors?
Different chip with richer fuel table in those rpm ranges?

It runs really well, gets 21-22 mpg on the highway. If I could tackle this problem it would be the perfect car.