I need help with a diagnostics on my vehicle.

On a recenn trip to Canada (280miles each way) the "check engine light" came on on my 02Disco. After checking with the local auto store for codes (autozone) I got the Oxygen sensor errors.

I then replaced the front O2 sensors. Also replaced the mass airflow meter assembly.

Engine light came back on.

New codes P0300, P0302, P0306, P0307 ( multiple cyl misfire, cyl 2 misfire, cyl 6 misfire, cyl 7 misfire)

I then replaced spark plugs and plug wires. Also performed oil change with engine flush (in case valves were stiking).

Latest readings are P0300 and P0307, but only when I rev my vehicle to 1500 RPM or above. I can have it on idle for ever with no "check engine light" coming on.

What should I replace now? Coild Pack? Rear O2 sensors?

Or should I get it inspected by the dealer? ($$$$$$$$$$$$$$)