gta probs miss

my gta has 30 k miles so it sits a lot.When it first starts has a little miss which goes away in bout a mile.Now when im really gettn on it when i reach bout 80 to 100mph it starts missn like fuel shortage sounds like little bakfires.hasnt really done it under normal driving tho.Las year put new fuel pump wireing assembly plugs wires.Any ideas i hate not bein perfect..Thanks dave