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If you have a V6 engine the labor to replace the spark plugs is 3.0 hours as the upper intake needs to be removed to access the passenger side plugs. On the V8 engine the labor is 2.0 hours.
For the V8 we charge 2.0 hours labor at $125.00/hour for the spark plug replacement. My dealer is located on the east cost (Tri-state area).