Yeah, you may be able to use transmission fluid for your power steering, but personally, I wouldn't. I would use the fluid that GM recommends.
I'm just not sure why you would purposely use transmission fluid in your power steering system when GM specifies power steering fluid... Just use what the manufacturer recommends. Now maybe if you were "stuck somewhere" and all that you had was transmission fluid, then maybe I'd use it, but otherwise, I just don't see why you would purposely use something other than the recommended fluid type.
Maybe you can use transmission fluid without issues - but why risk it?
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