[Ron61]

RZ,

The other guys have pretty well covered all but one thing that I have seen happen. A friend of mine with a MOPAR, excuse the non Cobra, had almost the exact thing happen and around 2800 RPM his shift lever would vibrate so bad it sounded like a snake buzzing. Then it would quite down as he got above that. It finally turned out to be his drive shaft had just a little twist in it. I seriously doubt if this is your problem but maybe it wouldn't hurt to look at your drive shaft and it's alignment.

Ron