Power Steering

My power steering didn't appear to be working, so I replaced the pump. Hoses are fairly new, so I re-used. After I started the car for the first time, the PS worked well for about 2 minutes, and after driving for about a half hour does not seem to be working at all. Is the control valve most likely the culprit?
 
Does your car of long tube headers? If so does it have the lowering bracket for the slave cylinder? I ask because if this bracket gets lose, it would be like driving without PS. This has happend to me a couple times. Just a thought to get you going.
 
Does your car of long tube headers? If so does it have the lowering bracket for the slave cylinder? I ask because if this bracket gets lose, it would be like driving without PS. This has happend to me a couple times. Just a thought to get you going.

I don't think I have long tube headers (I'm still familiarizing myself with this car). I will check that out, though.