OK, a dead miss is a constant misfire, you feel it all the time. There is a few things that can cause this Jeff, I will list them, but it will take some fault tracing steps to narrow it down.
I'm going to first suggestion, removing plug number 3, take a good look at it, make sure you didn't crack it puttin it in, (sometimes that happens) If it's not cracked, Get a spark tester or old plug, and pull the wire off cyl. 3.
Make sure number 3 is firing (ground the plug or spark tester to engine
metal) We want to make sure the coil pack is proving spark to cyl. 3. at all times the engine is running,
If we do not have spark to cylinder 3, see if the coil pack is arcing or "leaking" spark out the side of it anywhere, and you may spray it down with some water to help see if it's shorted out anywhere.
If we do have spark to cylinder 3, then you'll want to check compression on that cylinder just to be sure compression is alright, If compression is alright, check for injector pulse. with a noid light. If you are getting injector pulse, then swap injector 3 for number 2, see if your misfire moves from P)303 to P0302. If it does, then you have a bad fuel injector
Last but not least, if you don't have any spark to the plug, The PCM grounds the coil pack to provide spark for the spark plugs
, It isn't uncommon for the coil drivers in the PCM to fail. I know you have power to the coil pack if it's running, so I would suspect a failed PCM if you do not have spark to number 3 plug and the coil pack isn't failed.