Plugged fuel filter, and/or bad fuel pump in conjunction with possible crud in the throttle body. I would try a filter first, a pump second and then rebuild the throttle body third.
Make sure if you pull the pump, that all the rubber hoses are in good shape. Seen TBI chevys with the hose right after the pump have a split in it so it was always spraying fuel right back into the tank and couldn't build proper fuel pressure. It ran a lot like you're describing. But if you get that far into it, change the pump too. Quite a bit of work to go to, not to change the pump.