How many miles do you have on recumbent trikes? After several hundred miles, that wondering problem that frosh trikers have has melted away. It's because of old upright habits which don't translate, (at least directly), to recumbency, especially to trikes. First, there is the unconscious pulling back and forth on the steering bars. Then, there is the rocking of the torso which isn't nearly as efficient on a trike as it is on an upright. There are even long-time trike pilots who still do it. Take it from me, it is worth the focus to isolate the motion below the beltline from the torso. "Coiling," crouching closer to the pedals and even bending at the waist for high-energy sprints are helpful, but to dampen rocking, you might lower the gear, increasing the cadence, not drastically, but bit by bit, and notice the effect each time.
Hope this helps.