1995 Dodge Dakota Dropps dead after 20 min

Ok truck belongs to my mother who beleives in only putting gas in a car. Enough said about prior maint. Car came to me after 3rd break down to "get it running" It will start when cold and run fine for about 20-30 min then its like someone just cuts off the fire to the engine. All other electrical function is fine pleny of juice plenty of crank no go.

Checked codes popped for bad coil/Distributor

Installed new coil new pick up new button and cap
put in new plugs and wires (did an oil and all filter change while I was there) Also I jockeyed the main relays around (all same part #) and verified my fuses.

Test drive. Walk home

I can return to the car about 4 hours later and it will start and drive home. I have replaced everything up to the ECM but before I bit the big bullet I wanted to know if there was anything else I am missing. Is there a sensor that if hot or bad could tell the ECM to kill ignition?

Other info I think my Cad converter is bad and have a replacement that I have not cut in yet (along with new muffler) Also I noticed a small leak at the water pump which might be going out but gauge has never shown hot and I have checked for water flow its flowing when Tstat changes.

All help greatly appreciated pulling my hair out here
Sign me
Stuck