If start by ditching those iridium plugs, I've had them break down in under 1000 miles.
Only buy plugs from a dealer or m and p (somewhere reputable) as there are tons of fakes out there on eBay.
Then check caps, leads and coils.
There are only a few things in the ignition system to cause a miss fire.
He didn't actually mention Ebay, but i have had moody ones off there before that started faltering after a month. I won't use anything but Iridium now though.
I buy from these people who are legit, and reasonably priced.
https://www.gsparkplug.com/But as far as a misfire, there's more than you might think to cause it.
Bad fuel, water in fuel, air leak, blocked air filter, TPS breaking down/faulty, dodgy/knackered plugs, HT caps not screwed on tightly, HT leads need chopping at the ends as wires are pushed into outer casing, coils breaking down, unbalanced carbs, etc.
It's not as straightforward as you'd imagine, plus it could always be a combination of things too. For example if you balance the carbs with any of the other things listed not right then you are opening up a new world of pain.