The Ford Warranty and Service Guide states that 'A claim under the Ford Vehicle Warranty will also be rejected if a Modification is made to the vehicle by, or for you and such modification adversely affects the performance / compliance of the part in respect of which such claim is made.' I put that in the email and told them the Ford Mechanics could not even tell me how a CAI can affect Diff performance. The only reason I havnt had a custom tune was because of the warranty. Think I might book it into Real Dyno Tuning next week and get it done