[Trey's 5.0]

Car is lagging/sputtering really bad in every gear. Not sure what the problem is. Once over 3500rpm or so and WOT it runs like a champ. After driving 30min or so parked car for a couple hours went back out to start, would start up but then on idle down it would just cut off, took about 5 times to actually get it to start and keep running. Not sure what the problem is. Anyone have any ideas would be appreciated...