My friend's 96 Talon was doing the same thing and we switched it back to wires and it went away. I also have COP and have been doing some logs and in my log's after 4k the rpm line gets a bit choppy. I'm thinking I'm dealing with the same issue. I have a couple ideas:
If your still using a plug and play I'm assuming your running the stock Ignition module, as was he and I. I think this is where the problem is. The stock ignition module is built to fire two coils in a waste spark set-up. When you install a COP the ignition module is now firing two coils at once, well two coils take more power and I'm starting to think that the ignition module can't handle the extra load at high rpm's. At idle everything is smooth, since spark output is lower. That's what I love about the COP, idle is sooooooo smooth.
I'm going to try swapping mine out, if my choppy datalog's go away, I'm going to experiment with the COP and see if I can figure something out.
I know that you can run an aftermarket ignition module, but I know for a fact the AEM box is way too unreliable, and MSD doesn't really cut it for COP. Right now I'm wondering if you ran two stock ignition modules wired in parallel to make up for it? Maybe, any thoughts on this?