1998 BMW 540i bank 2 misfiring

I replaced my valve cover gaskets this past summer because of oil leaking into the plug wells. I recently replaced all 8 spark plugs as well. Using the Peake code reader, the codes I am getting are "misfire detected, cyl. 5" & cyl 6, 7 & 8. Additionally, there is a "random or unknown cylinder" misfire along with "catalyst damaging" on cyl 5, 6, 7 & 8. I've swapped the ignition coils & the misfires are still on cyl 5 - 8. Also, the pre-cat O2 sensors were replaced about a year ago.

The check engine light flashes during wide open throttle beyond 3000 rpm & it struggles to rev past 4000 rpm - I took my foot off the accelerator after a while, thinking that I might do more damage if I tried to push it beyond 4000 rpms.

Thanks in advance.