Car sputtering and shuts off

After changing my spark plugs the car started sputtering and losing power when It was trying to change gears. It would eventually change gears but give you a big jump when it did like something was clogging it. I changed the fuel filter hoping that would help but it did not. It actually started making the car shut off all of a sudden when driving. I would have to step on the gas constantly when driving to keep it from shutting off. But the funny thing is when it's in park it will not shut off, it will keep running at low rpm. I know there is a blockage of fuel somewhere but I do not know where.