Poor idle and off-idle performance after distributor swap

To circle back around after a couple weeks of driving, my erratic timing issue still remains. Car runs very well, idles strong and pulls hard but I am missing power and economy due to this timing issue. Timing appears to wobble by about 5 crank degrees. Idle rpm, vibration and sound all agree with the 2 timing lights I have checked with. I currently have timing retarded below what it wants (set at 10 initial, wants 15-16) for safety until I diagnose this problem.

Balancer does not appear to be slipping.
Have changed caps, rotor, plugs, coil, no change. ignition is very strong and plugs are clean. Fires right up with ease. Don't think it is spark related.

The Pertronix pickup assy is firmly mounted, vac can is fixing its position and there is no wobble in the advance plate.

The only thing I can think of that would cause this is the distributor. It is a factory distributor with a Pertronix Ignitor 1 as the trigger. Did some research, not sure if the Pertronix is known to cause erratic timing.
My theory is that perhaps the advance springs are weak or failed somehow, and allowing advance to bleed in at idle, albeit very erratically. I looked at them today, both advance springs appeared properly seated and in good condition. This jump in timing is consistent through the rev range, but is most noticeable at idle.

What am I missing here? I hate to just throw parts at it. The car runs so well, I can just imagine how much faster and smoother it will be with the timing locked down and not wobbling by 5 degrees. I have contacted Ray about rebuilding a 2nd distributor, would be nice to have a spare.