Might be bad news, but your sunroof is done for. Mine did the same exact thing. The reason it only goes up on one side is because a little plastic part broke in the arm that raises it. It's not serviceable and I was never able to find just the separate parts.
The reason it only goes about half way closed and really slow is the motor. That part can be replaced, but since the other part is fubar you might as well replace the whole unit.
I was bummed when it happened. I really loved the sunroof in my GVR4, it really makes we wish I had a sunroof in my GTO.