I know they recommend atf 4+. The guy who had my pickup before me cost me a rack and pinion, power steering pump and new lines.... So i would NOT recommend leaving it in. I believe the reasoning behind this is viscosity, at lower temps the atf wont get thick like the power steering fluid will.. when the fluid gets thick the pump cavitates and causes issues. as far as flushing i would think the best would be pull of the lines let it run out, maybe jack up the front end and manually push the wheels to empty the rack.. im not expert just my thoughts and experiences.