I have two engine problems that are giving me fits-
1. Engine miss during part throttle accleration - no miss at constant RPM or full throttle accleration. No codes in computer
2. Intermittent (seldom) sound from engine like slipping belt - serpentine belt on or off. Maybe the timing chain?
The one time I've seen a part-throttle miss was on a car with an extremely dirty air filter (not mine, of course!). Check your filter and run a bottle of high-quality fuel system cleaner through it and see if that does anything.
54k isn't a lot of miles for an '02. Has the car been sitting for an extended period of time?
The slipping belt sound might be exactly that. What kind of shape is the belt in? How about the tensioner? Occasional belt slippage can be addressed by putting some belt dressing on to help the belt get traction.