Typically with bad coils you feel the misfires, however, I wouldn't rule that out. At 176k, it could be a slew of issues. The cat(s) could be getting plugged up and/or O2 sensors going bad. Have you done a top-engine clean? It could be carbon build up affecting the upper rpms.
I've seafomed it and that's about as far as I've gone with cleaning. I've only got 1 cat on the car right now and that's the primary cat on the manifold. I'm leaning towards the carbon build up and/or coils because it starts the flat spotting around 3,750 and does it all the way up as far as I know (I grab a gear at like 5,500 at most).