As many truck and SUV owners know, the performance of the transmission is a big part in how confident you feel behind the wheel. While only a single part in a complex powertrain, the transmission is the glue that links an engine to the road. When the transmission hesitates, the entire vehicle’s performance suffers. A great vehicle needs an equally great transmission.
After only a few minutes behind the wheel it became obvious that shifts are quicker and smoother than the past generation 6-speed. Having two more gears allows the engine to stay in the sweet spot of the RPM range more often. Tip into the throttle and with no drama the 8L90 quickly snaps to the right gear.
However, the most noticeable change is how well shifts are managed by the faster next generation transmission controller. Dependable and crisp transmission performance is a benefit in any situation. A slight bump in fuel economy is the icing on the cake, allowing for a +1mpg bump in fuel economy.
Under full throttle we found gear changes effortless, quick, and solid. Under light throttle we could barely notice the vehicle had shifted at all. Where the past generation 6-speed sometimes gets confused or doesn't shift as cleanly as we’d like, the new 8-speed was always seemed on point.
Unfortunately, we're slightly surprised to see that manual shifting with the 8-speed hasn't changed. Commands to select a specific gear using the shifter stalk are still only a suggestion, with the transmission controller having a final say. In our short test, shift requests sometimes took seconds if the truck didn't agree with the gear we requested.
We drove an 8L90 equipped 2015 Sierra Denali and Yukon Denali on urban streets during rush hour. We did not get an opportunity to measure fuel economy.
While only available with the 420-horsepower 6.2L EcoTec V8 during model-year 2015, expect this 8-speed to be available in the rest of the full-size truck and SUV line in the near future.
When we have an extended amount of time with another 8-speed truck we will report back with fuel economy figures and more driving impressions.