The rubber strips description is what I'm experiencing, but it seems to happen most often under very light throttle, only enough to maintain a cruising speed. If I get some time to experiment, I will be better able to come up with the exact conditions, but I believe the tach is under 1500 RPM at when this happens. I cannot say for sure yet if the shudder goes away on its own after a few seconds, or if I'm subconsciously helping it by applying just enough throttle to satisfy it.
How long does the transmission take to adapt to new driving scenarios? For example, the first part of my way to work is stop and go, and essentially racing to the next stoplight under hard acceleration. Then once on campus it's about a mile of 30-35 mph cruising with little to no throttle input and few stops. Most of the time, this is when I will notice the shuddering. Could it just be that the program has not yet adapted, and is still expecting me to accelerate as I had been?