So basically, I have a new motor, new alternator (1500miles) and I did my first 7k pull, and well....my volts started going down steadily all night after that. And eventually ended in the car stalling and not starting back up.....

This would be my alt I assume? Did I over spin it or something?

 

Yes, it is your alternator, and yes, you probably did over spin it. They don't like high RPMs at all. I have mine purposely underdriven (stock diameter crank pulley, underdrive alt pulley) to keep the RPMs down. Do a search, and you'll find some good info on here.