My Current cm871 situation

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A failing exhaust gas pressure sensor or plugged pipe to it can contribute to a dropped valve.

Other factors can be simply the age of the cylinder head, valve seat wear, incorrect vgt/engine brake mapping, restriction in the exhaust.

I have only ever known 1 truck to have a McBee kit put through it and it ended up getting rebuilt with a Cummins kit 2 months later due to heavy oil consumption. There's nothing to say it wasn't assembled poorly the first time but I would probably never trust a non-genuine overhaul kit anyway.