Stalling

[jetstream87]

A while back I had the car throw me a P0302 code in which cylinder #2 was misfiring, after a while the code went away. There are occasions when I can hear a light thump sound and a bit of a shake when I turn it on in which the code doesn't come up. Yesterday I was driving to the store in which I was running the car about 25 mph and the RPM started to drop a little like it wanted to stall but kept going, on the highway I can feel the stall a bit but the car kept going. I took it home let and after a while I took it for a spin and it ran smoothly. I went to the grocery store came back, turned on like a charm, while driving back again the light stalls started but it happened about 3 times, got into the on ramp of the highway and it wanted to stall where I can feel the car wanting to pull back.......What can it be? I have changed the spark plugs, not leaks, no hissing sounds when the engine is on and idle. Do I have to clean the throttle body? Can it be the gas filter?