Coils can be some the most cantankerous things.
I have had a few that would idle well, but give it some
gas and they would die. Put a new coil on, and run it through the roof.
Sometimes the problems would not show up, til they were up to
operating temperature, then show the problems you describe.
Other times they would die, til they cooled off, then you could run
them til they heated up again. I have noticed, for the most part,
that if a coil does not just die without warning, the upper RPM's
will be where you notice the degradation first. Hope that helps.
Marc