Power steering problem 1998 Buick Regal

Serpentine belt broke due to tensioner bearing freezing. Drove it for another 4 minutes and stopped before it reached max temperature/redline. It was stopped in a bad area, so waited for an hour plus, then drove it out of the area and again stopped before redline. Next day drove it another 5 minutes plus but stopped before redline. Replaced the tensioner the power steering started having pulses of assist and then none. Drove home for two hours with steering problem. I think it is the pump, how do I check to see? 1998 Buick Regal 45,000 miles. Still runs good, just the power assist problem with the steering.