Make: Mitsubishi
Model: Magna / Verada / Diamante
Engine: 3.0 litre V6
Year: all 12 valve

Engine miss at high speed running and / or high loads. Problem gets progressively worse as time goes by.
Distributor caps on these vehicles (both genuine and after-market) have a tendancy to track-out both internally and externally, especially when wet. Often mis-diagnosed as faulty leads, dirty fuel injectors, faulty air-flow metering etc.

Check for light blue-grey marks inside distributor cap (most especially where the internal "cross-overs" change direction and/or pass near the edge of the cap) and replace cap if the marks are found. Caution!!! The distributor cap can only be removed when the rotor button is facing the left hand side of the vehicle.