Question: With EST disconnected to set initial timing, should the initial timing move with the throttle held open at 2000 rpm?

Long version:

I recently bought a new Cardone dizzy with cap/rotor/everything and new AC Delco coil for my 88 5.7L TPI as the old one was missing quite badly under load.

New one looks identical, perhaps .5 to 1mm longer overall (it's not quite as snug on the intake).

Fires up, runs ok, car still doesn't run right, like there is a timing issue.

I have timed the car correctly several times, but the timing moves around 1-2 degrees at idle in either direction. The most concerning thing for me is if I hold the throttle at 2000 rpm or so with the timing light on it, the timing will actually pull all the way back to maybe 12-16 degrees BTDC (after settings to the 6 degree BTDC spec).

I have put the old failing dizzy back in, using the new cap/rotor/wires/coil and it is dead steady during initial timing, and moves maybe 1 or 2 degrees but only when I crack the throttle.

It's my assumption there must be something physically wrong with my new dizzy, but am wondering if this is expected behavior for some reason?

Not my daily but for now I basically set the timing on the new dizzy to be 6 degrees BTDC with the throttle cracked....