Intermittent crank no start

Hello Everyone, I'm new to FABO so I'll try my best to present my issue and what I've done so far.

I have a 73' Dodge dart swinger with an automatic slant 6 that was being used as a daily driver until this issue started.

Recently the car has had a crank no start issue. When I do get it started in runs very smoothly and then suddenly dies after roughly 5 minutes. Sometimes it will idle really high but then eventually die the same way.

The battery's voltage reads 12.50v when it's sitting and 13.25v if I get it running. I have re-grounded the ECM and voltage regulator. I used electric parts cleaner and cleaned / brushed all of the connections along the electronic ignition system that I saw. I brushed the terminals in the distributor cap and checked the gap between the reluctor and pickup (only visually, I didn't want to mess with it if I didn't have to).

coil positive to ground key on I get a dim light, crank I get bright light
coil negative to ground key on I get no light, crank no light either

When the car does start up I notice that the spark is very weak. only jumps about a 1/4 inch or so. Coil + reads 6.88v coil - reads 3.10v.

Any help would be much appreciated, I hope this gives you all enough information to help me.