Pulls hard and then quits...

Yeah, I have to agree it's a fuel delivery problem. Stock pump?
A couple of ways to check it........hook up a fuel pressure gauge between the pump and the carb, of course you have to be able to read the gauge from behind the wheel when it quits and see if the pressure dropped off right before it quit. or you can slid it into neutral, shut down the ignition as quick as possible and coast to a stop (not recommended if you have PS or power brakes). Then check to see how much fuel is in the bowls, they'll probably be dry if it's a fuel problem.