I'm still betting 100% that your mech timing is off.
Triple check it and try retarding the mech timing by a tooth, should bring you back into the right range if you're all the way advanced now.
I tried this on the previous engine when the ignition timing still could not be set. The car ran worse.
The mechanical timing is where it should be. Like I stated above, when I double, triple, quadruple checked it, when I turn the crank so the cams line up, the TDC mark on the pulley is maybe half a centimeter past the notch on the timing belt cover...but I can turn the crank back enough to line it up without moving the cams. If I set it a tooth off either way, the TDC mark is way off the notch.
Mostly I'm looking for other suggestions. Mech timing 100% sure correct.
What, other than mech timing, can cause ignition timing to be off?
The ignition timing also fluctuates with the RPM while it's running, it's idling 100-500rpm.