Intermittent stalling while drive but not when stopping

Two weeks ago, car stalled driving 55 mph after approximately 20 miles. Restarted and got to work. Did the same on way home. I had gotten gas just before this. Put gas additive in tank and drove fine for over 2 weeks. Yesterday stalled after approximately 4 miles with quarter tank of gas. So limped into station and filled with gas. Stalled a few times, then drove fine over 24 miles into work. It stalled again coming home from work after 23 miles. When stalls, it stutters a bit then stalls. No check engine light comes on and don't see any codes.

Where do I start?