power steering problem

[Mhannink]

ok so my budy has an 04. 5 dodge with the high output cummins. a couple weeks ago we where spinning dounghts and his power steering crapped out. it would only provide power to the steering and brakes if the rpms where up about 1500 or higher it would also make some funny noises when on the brakes and idleing. thinking it could only be the pump we replaced it. now he has the same problem again only this time it didnt happen after some high rpm dounughts. we are thinking it could be the hydroboost. the hydroboost has always had a little bit of oil on it. only ever enough to collect dust and not enough to really be a leak. any body have any ideas what it could be?