Since it is happening only at that speed, it leads me to think it is related to something other than the engine. The engine doesn't know the car's speed. If it was a specific RPM where you notice it, it would do it at any speed but specific to a set RPM.
Pay attention to see if when you feel it correlates with a specific gear the transmission has shifted into. Also, if you have a live data scanner, I need you to check the short term fuel trims when you feel it happening (throttle steady).
Let me know.
Sunday, December 22nd, 2019 AT 7:37 PM