96 Lumina Hesitation

Hey all. Just recently bought a 96 Chevy Lumina. The guy that sold it to me said it was his grandmother's, and had been sitting mostly idle for a few months. For the first day after purchasing it it ran fine - now, for the past 2 days or so, it has had major hesitation problems. It feels very similar to when you are running out of gas. It comes and goes intermittently, at times i can drive for half an hour flawlessly, and at times it hesitates every 20 seconds to a minute. It often begins appearing while driving at high speeds, but continues afterwards at lower speeds. It also seems to be worse going uphill. I replaced the fuel filter, which was somewhat clogged, most likely from sitting so long, but the problem has persisted (though it seems less than what it was). Also, i just tonight noticing a slight knocking sound from the engine that wasnt there when i first purchased it. Thoughts? Also, i am not the most advanced when it comes to cars, talk dumb to me. :P

May have water & or fuel separating in tank, & or clogged filter in tank (there is one on the intake end of the pump). As for the knock, need to know much more about that.

If the car has been sitting for months, change the oil. Yes, oil has a limited life once it's in the sump and been run. Acid formation starts as soon as the engine has been run and the oil gets fuel and moisture contamination. Instead of a multi-paragraph missive describing the chemistry of emulsification, anaerobic oxidation, and hydrogen conversion to hydrochlorides, spare yourself and just change the oil. Even if that doesn't solve the knock, it will prevent any further soft metal damage in the bearings.

As for the hesitation, changing the fuel filter was a good idea. Now check the air filter and test the fuel pressure.