Okay, here's the story.

I go to start my truck and it starts up, and instantaneously there is a loud pop...

I drive her to the womans house and we start heading to my place and my tach starts to go crazy and I notice the headlights dimming. On the way home I have to turn the headlights off just to keep the truck running. Now it'll barely run in idle, as soon as I put it in gear she stalls.

I'm thinking some kind of selinoid somewhere ?

Truck is an 87' M4 I6

 

it sounds like you blew the alternator and/or the fuseable link. The tack runs off the frequency generated by the pulse drawn by the coil. Your battery isn't charging any longer and it takes all the juice you got in it to keep the engine running.