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engine misfiring on down side of rpm’s and stalls at times

I replaced coil #3 on a 1997 maxima two months go due to misfiring, the engine ran smoothly since. Last week I felt the same symptoms as two months ago and I am not sure what is causing it whether there is an electrical short or oil leak onto the spark plug or something else. Thanks

so far they replaced the catalytic converter, fuel pump, fuel filter, and cleaned fuel rail. Engine compression is 160 across all four cylinders. New plugs, coils and  igntion module. Could it be a sensor? vehicle has 70,000 miles and oil changed every 3,000  thanks.