Hate to start another thread ... but.. help !

Ok so I have cruised through many topics on this subject.... and still am kinda at a loss. Maybe someone with some electrical knowledge can lead me down the right path ..... please !

Heres the scoop.....

My car suddenly developed a issue where it will just be running fine and then die... kaput. Saw the coil was leaking pretty bad.
Replaced coil.
Same problem still exists.
Find I can start the car in park / neutral with no problems. Fires right up.
Runs and idles pretty good in park/neutral.. but have noticed a slight hiccup in the idle. So now I put the car in gear drive/reverse and it will idle about 10 seconds and then suddenly die. Kaput. Put car back up in park... hit the key an it fires right back up. Put car back in gear... dies. I have eliminated any fuel issues. So I started using what little electrical knowledge I have and found that the battery was pretty much junk... hey.. it was 10 years old. So installed new battery. Still has same problem. (didnt think that would fix it.. but hey... ) Ok so battery running proper voltage. Alternator at proper voltage. Check voltage at coil.... blaaahhhh.... 4 volts... and lower. Hmmm.... ok... for giggles I switched to another known good coil thinking my new msd one is junk. Nope... same ... 4 volts or less. Thats even on start up folks. So... what the heck ? I changed out ignition boxes (just standard chrysler black box. The alternator is new, battery is new, regulator is new, and the ballast is like a year old. I am a idiot when it comes to testing things electrically so ya all have to speak like I am a dummy. Is it possible the ballist is bad ?? Even if not very old ? I have a new one.. I just need to install it... but if that doesn work... where do I go ? ?

74 Plymouth Duster.
360
Mopar dizzy
Mopar stock electronic brain box.
Mopar stock regulator
MSD coil
Stock style ballist.

Keep in mind it ran good before on all this (except the coil) and now problems...... any ideas ???

Thanks in advance !

-RPM