Hello I have 99 Grand Prix naturally aspirated. Code in my car says I have a vacuum leak. Is it my o2 sensor? Ir where could it be coming from. Also I am thinking of doing a transmission rebuild car has 170,000 on it . Rebuilt engine 5,000 ,miles ago. Any suggestions. I think my clutches finally need to be replaced. Car runs on full synthetic oil and trans fluid. I have straight cat Borla exhaust system. Cold air intake. 180 t stat. Also my gas gauge went out. Sometimes it says full other times it says empty . Any suggestions?.