According to reviewers at AutoTrader.com and MotorTrend.com, the GMC Sierra Denali models operate best when loaded up and tend to bounce too much when empty. Otherwise, the truck does the job for which it was designed, with reviewers generally satisfied with its capabilities.
The 2015 GMC Sierra 2500HD is reviewed as a very powerful, functional truck that can tow several tons of weight. It comes with features such as a rear camera and a vibrating seat to warn of lane departures. Criticisms with this model include the camera's low resolution as well as a "lethargic" gear selection compared to competing models when working with a large load in the back.
The 2014 model is described as driving almost like a luxury car, with very good braking and a very powerful engine. The truck can tow large payloads without any signs of struggling with the weight. Again, the criticism is with the towing gear shifts, though this time it is due to an inconsistent transmission.
Overall, GMC Sierra Denali models appear to run very well according to truck critics. They are fairly powerful and have excellent handling for trucks of their size. They have a fair number of modern technologies, such as USB slots, and the technology includes well-tuned collision warning systems, depending on the model.