The GM pump should be a saginaw pump, and it does produce more pressure than the Ford pumps which could be a Ford/Thompson or maybe a Eaton pump. However Ford did use some GM Saginaw pumps on some of the Mustangs in the 70's as well as on some of there cars with Racks, so this probably isn't your problem. There is a pressure relief valve inside the Pressure line on the Saginaw's pumps and this can be changed to change the pressure. Hopwever with that said from what you state this system did your problems lays somewhere else besides pressure. Sounds like you need to diagnose this "Self Steering" problem first.

Roland