What caused this?

How much gas did you have in the tank at the time? Are you sure you weren't just running out due to fuel level? Does the car come back instantly after letting up or does it run rough for a while after letting up on the gas? Hope you get it figured out. Probably alot harder to nail down since you have to hit 70 or so to see if it's gone. I would think a stock fuel pump would be fine on a mild build. There are members here that use them all the time and have no issues with fuel starvation.