More updates....

Replaced MAF
Replaced rear O2 sensors (previously only replaced front O2 sensors)

This made a small change - I can run between 65-75 MPH without any misfire codes being thrown. The engine is still stumbling slightly in this range (3000-3300 RPM). Stumble happens when at no or slight throttle and I am either letting off the throttle or accelerating.

It is still throwing only misfire codes across all cylinders at lower RPM's and at excessive highway speeds, again under the same throttle conditions as before.

Next steps (this weekend) are to:

Replace Vanos solenoids
Replace Cam sensors
Replace Crankshaft sensor

Vanos is not making any noise, and doesn't seem to be causing other typical symptoms (rough idle).