I have a 2003 GMC Envoy w/142,000 miles. Sometimes it is stuck in low gear for the first 4 miles. I checked the internet, it stated that my year vehicle is known to have transmission problems in 3rd gear. I went to the dealership, they changed the trans oil, but same results. I took it to Aamco, fearing the worst, but it was the opposite. They did a diagnostic check and said it was just a sensor, they replaced the sensor and my transmission works fine and at a fraction of a cost for a rebuilt transmission. They could have ripped me off by re building my transmission, but they only fixed what was wrong with the vehicle. It was nice to have an honest automotive repair shop.