I had a similar issue like that I would be leaving the parking lot letting the fast idle pull the truck up to speed then add alittle light throttle then it would surge off and on some. Went to a aftermarket throttle body and haven't notice it since.
The fix has been releast and the technical service bulletin is #PIP5250B.
more info here
http://www.motortrend.com/roadtests/oneyear/trucks/1503_2014_gmc_sierra_denali_1500_4wd_crew_cab_review_update_6/
Those that having some issues the fix has been released not to long ago.
http://www.motortrend.com/roadtests/oneyear/trucks/1503_2014_gmc_sierra_denali_1500_4wd_crew_cab_review_update_6/