I have the same EXACT problem with mine, 2014 Impala

The engine does Die a little during the time it is losing power. the TACH goes down, some RPM, then goes back to normal, then repeats itself, a number of times. Hope this helps ! The transmission seems NORMAL at this time. Can't tell if it's choking or not.Just the engine breaks up between 1800 and 2400 RPM.

Are you a mechanic, and where are you located ?