1997 Mustang Power Steering Problem

My Mustang was grunting occasionally when parking etc. Last week when pulling out of a parking spot most power steering was lost. The wheel would shudder when turning it. Drove it home, very close, fluid level OK no leaks but very little power assist. I took a shot at it and replaced the rack and pinion with a used unit. Started it up and virtually no change. Tried a few lock to lock to expel any air the power available decreased. Shutting the engine off and looking inside there was a little bit of smoke coming from the pump pulley. The plastic pulley had separated from the steel center. Replaced the pulley the shuddering is gone but still almost no assist. Replaced the pump, same outcome. I'm running out of things to replace.