2001 Dodge Caravan Grand Caravan intermittant hesitation

2001 Grand Caravan, 2 wheel drive automatic, 3.8 L, hesitates intermittantly. Occurs most often during first minute of driving during first acceleration, but can also occurs during steady driving at 30 mph to 70 mph. Engine never completely stalls, although occasionaly during steady running feels like it stalled briefly but then restarted. Duration is usually a couple of seconds but occasionally can be rough for half a minute. Doesn't seem to matter if warm weather or cold, wet or dry. Have changed spark plugs, wires, air filter, fuel filter, fuel injection filter, have checked ignition, and there is no diagnostic code. Any suggestions where to check next?
Thanks