If you have a TB IV with a stock v8-24 module, full timing advance does not come in until around 3700rpms. If you are 33* at 3000rpm, you could easily be at 37-38* at 3700rpms---which is too much.
I seen the timng tables recently from a innovation hp 500 efi and I was surprised to see it was set for 38 degrees at 5000 rpm and 100 map (0 vacuum).