In that low a gear, you will come almost to a stop between downstrokes, so that progress is a series of leg burning bumps.
This makes a lot of sense to me, CFB. It feels like I speed up a bit (maybe 4-5 mph, lol) during the downstroke, then slow down to a near stop while pushing the other pedal forward into position for another downstroke.
The inner math-geek in me thinks about this as a sinusoidal wave with speed as a function of time. During pedal strokes, speed peaks. Between pedal strokes, speed troughs due to drag factors (wind, road resistance, gravity). As the drag factors become more significant, the troughs deepen. At extremes, speed dips near zero and what usually works may not work anymore. Your approach of sitting down and focusing on evening out the pedal stroke would reduce the amplitude of the wave.