The first thing I'd do is this ^^^^^How did you check the COP and fuel injector? These are normally difficult components for the home mechanic to "check" correctly.
Most of us have to resort to replacing them or swapping to a different cylinder to see if the problem follows the part.
The COP boot insulator could be bad allowing spark to escape. Autozone (Durlast) makes a set of (8) replacement COP boot insulators that cost less then a single replacement COP.
As for what else COULD cause a misfire, a base engine problem. Run a compression test and/or cylinder leak down test.
It's NOT excessive EGR flow as this would affect multiple cylinders. For the same reason, it not low fuel pressure.
Consider a fuel injector cleaning/flow test service such as injectorrx.com. Once cleaned, they are as good as new. Much cheaper than buying new.