Had codes read at local Auto Zone: #3 cyl misfiring, changed spark plug,

Engine size & type would help answer that!!!!.... However.. Here's how it can be done... Swap # 3 coil with say # 1 coil to see if misfire follows the # 3 coil.. Then you'll know!!!!.. If misfire still on # 3, then start hunting for other soulitions!! .. *After coil swap*... IF misfire is obvious at idle, can remove each coil 'wire connector' and put back on, one at a time, to see IF engine responds.. OR NOT!!.. IF NO engine response (misfire stays same) that is problem cylinder!.. IF misfire gets worse, then check another coil!!.. > Capish???... NO... You ain't going to get shocked!!!!!!

No. Switch the coil pack with another one and see if the misfire moves to that cylinder. If it does, that's a good indicator of a bad coil pack.