Go Back to the service dept, make a point of one of the tech's going with you on a test drive
tell'em you want a explanation written. if there is a quirk in software or even an issue on the build out of a mechanical device, Most of the time the factory will send out tech reports on the problem. dont let'em walk on ya...push your chest out and roll the corner of your lip over a tooth
There must be an explanation !!
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Is your Pony Car a Auto or a Manual?