Looks like your suspect driver works well with low speeds.
That tells me it is not damaged.
Let us have some specifics.
What are the motors you are using?
Are they 1.8 (200 step) or 0.9 degrees (400 steps per rotation)?
What is their max current rating?
Did you use a different microstepping for GOTOs? That is one way of speeding up slewing.
Attach the config file that you used last.