Misfire code

Car has been running rough at low speeds. At first I thought the CVT transmission was not down shifting, but ruled that out after taking to transmission shop. I was told that the crank sensor was bad and needed a tune up. Showed occasional misfire on cylinder two prior to changing all plugs and coil packs. Now car runs like a dream when first started and cold, but after fifteen minutes it starts running rough and now shows cylinder one misfire. Is it possible to get a bad coil pack? Are there any other reasons that the car would start misfiring after the engine warms up? Water and oil are good and show no signs of mixing, did a radiator pressure test and had no problems.