To wrap this up, original ETR would not adjust and output air never got colder than 52-54°.
Installed new Mahle evaporator temperature regulator and vent temps are now 44 to 46° (stock setting) even at idle in bumper to bumper Manhattan traffic. I do have a nice parallel flow condenser and a fan / fan clutch from a 560 SEL.
The ETR was the problem all along.