A few random thoughts...

If it were the timing belt, it wouldn't run right at any rpm.

You don't need a new coil pack to play "musical chairs", though the random misfire code isn't pointing to a specific coil pack, which makes it hard to know which one to switch first. (to see if the misfire code moves with it after resetting the ecu)

Any unmetered air getting into the system via leaks in any vacuum controlled system will wreak havoc & throw "codes-a-plenty"...

As a last, or maybe first resort, try to find a VX Bro or Sis who is sympathetic to your problem, & switch ECU's, to see if that's the culprit...