1999 Chevy Lumina Fuel Problem?

This car has been behaving badly lately, starts hard sometimes but still gets going, just like it has to turn over an extra time instead of firing right up, and when I'm driving it accelerates a little sluggish sometimes, or it's like there is a little catch or a sputter in it but then it runs fine, it's had the plugs, wires, and coil packs, all recently replaced. Fuel filter, or pump, I dunno? And how do I check this stuff?