1996 Pontiac Grand Prix My 96 Grand Prix still hesitates an

Over all it's been a very good car to my wife and I, but over the past 3 months or so we've been having some problems with the car Stalling! Or just dying out while driving. (It always started back up.)
On Tue.7-28-2009 I had a brand new Fuel pump and fuel filter installed, plus new Ignition control module and new spark plugs and plug wires. The battery and the alternator are six months old. After all that repair and new parts put in, YES! It runs so much better, but? I noticed it still hesitates and stumbles slightly. The Air Filter is K&N and is fairly new, so I'm wondering if maybe : installing a new PCV valve and new Throttle position sensor would help. Thanks for your help.