760twag vacume pump?

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there is a vac booster on mom's 760t that has not worked since we bought it (4+years) . does she need it ? new problems make me ask brakes are hard(more pedel presure needed to stop)rough idle&stalls if you excell then let off fast.compleet tune did not help'so please help me help her. if i need a pump where can i get one : thank you trent