Greg,
If you have a second 6200 you might try a quick impeller swap before you send it in. Obviously, if it works with a known good impeller but not with the original, the motor and driver are good and there is still a problem with the impeller.
If you have one of the older model impellers there are several possibilities we haven't talked about. (The older model impellers have a white plastic piece between the "propeller" and the magnet.) If you followed Roger's instructions in his sticky at the top of the forum, you should have completely disassembled the impeller assembly including the removal of the two small black plastic "brakes." I'm going by memory here, something that gets more dangerous every year, but that white piece should smoothly rotate on the impeller a fraction of revolution and the "brakes" should extend when rotated in one direction and retract in the other.
Thinking about shuddering, is there a red O-ring at the base of the impeller thrust bearing (the plastic piece that was stuck)?
Also, when the impeller is fully inserted into the motor block there should be a collar (bearing) that sits flush with the face of the motor block. In other words, when looking at the impeller sitting in the motor block the amount of side to side wiggling should be minimal.
To bring up an obvious point - I assume the "propeller" is not badly damaged.
And, to follow up on something from my previous post, I assume that the hole up through the center of the impeller is completely clean (similar to what you'd find on a traditional pump where the shaft would go).
And, to finish up, yes, it is Austin Texas.
http://reefcentral.com/forums/showthread.php?s=&threadid=1241409&highlight=austin
Tunze USA
305 Victor St
Austin TX 78753
I'm sure Roger will be here soon with the definitive answer.
Paul