I have sort of the same symptoms, but I've only seen it at idle.
It'll idle along at about 1600 RPM, and every once in a while, I'll see it jump up to 1900 RPM, but I don't hear the engine speed increasing.
I haven't noticed this on the road at higher RPM, because I don't look at the tach when I'm on the road, and I've only got about 18 miles on it so far.
I'll be sure to check the battery cables.