The GMC Sierra 1500 was equipped with the 4L60E in early models, and 6-speed 6L80 in later models and 8-speed 8L90 in 2015+ models. But they aren’t without their problems though, so let’s look at some of the most common GMC Sierra 1500 transmission problems, look at cost estimates and figure out what you can … Continue reading GMC Sierra 1500 Transmission Problems & Cost | 4L60E | 6L80 | 8L90