Surging And Cutting Off

I have a 1990 crown Vic with a 5.0, lately after running for awhile and shutting it off, then cranking it back up it would seem like it was starving for gas. After holding the gas pedal down half way, it would smooth out. Then while driving around 45 mph it would start surging, and at times it would stall while driving. At times it surges and don't stall, and at times it would run smooth and stall. Has me baffled. Any help would be appreciated