Any ideas on what the heck is going on?



Check the voltage across the coil with the key in the "run" position when cold and you're getting a good spark. Check it again when it's weak and the motor dies. If the voltage is the same then the problem is for sure one of the ignition parts or a bad ground. Remember the ignition box case has to be grounded to the firewall or other good ground. Same for the frame/firewall to engine ground strap. Check the ignition box case to the engine with an ohm meter, you should see .4 ohms or less.