GM Power Assist Recall
This bulletin applies to 2014-2018 GMC Sierra 1500 and 2015-2-18 Yukon vehicles. General Motors is recalling certain vehicles because the amount of vacuum created by the vacuum pump may decrease over time.
As vacuum drops, the brake assist decreases, increasing brake effort, extending the distance required to stop the vehicle.
Apparently the fix involves reprogramming the electronic brake control module.