Power steering problems??

[Imation]

Hey i just a question about the power steering on my 1990 GTS-T

I was driving along and my speedometer broke about 30sec after this happend my steering wheel got really stiff.When i stopped and turned off the car then quickly restarted the car. The power steering was fine again then after about 30 sec of drivng it gets stiff again.

I though it was the powersteering pump to i checked and it seems to be working fine no weird noises and u can see the line flexing when u turn the wheel so i believe its working. Then i check the belt the belt was REALLY tight to i loosend that as much as i could with it still rotating the pump pully fine. I tryed re setting the cars ECU, and check the PS fluid for any metal or debrie

Could this have something to do with the broken speedometer?? Or maby a broken pressure sensor?

The strange this about this is as soon as u turn off the car and turn it on it works great again and will continue to work as long as ur not in Motion!!!!

If anyone has any insight that would be great.Dan