2008 Mustang Gt - No Steering at High RPM

I had another thought come to mind, I used to operate a International Military Tractor out on the family ranch, it was bought from a base and the drilling rig cutt off the back where it connected to the PTO and converted to a normal Gannon and Teeth setup for plowing our pastures. It was a diesel and has full hydraulic drive system with 2 speeds on the reduction, it is capable of about 35 MPH, anywho its power steering is very simular to how a car or truck operates, and one time when it ran low on Hydraulic fluid the steering locked up solid, the wheel was literally stuck in place, not even muscling it would move it, and adding fluid fixed it. I wonder if the issue could be similar.

I cannot find the model of our tractor, but it was a custom build for the military with some sort of drilling rig that doubled as a crane originally on the back which was PTO and Hydraulic powered, but it looks nearly identical to this International 660 but ours has extra hardware attached here and there so the 660 was probably the base they added parts to when they made it fit the military's requested capabilities, ours also runs heavy duty truck tires on the front instead of the tractor wheels and tires seen here. The engine looks identical based on its side that is visible, but ours was all dingy camo green flat colored and chipped/worn quite severely.
http://gauer001.net/imagesia/1976RWBtractor-50.jpg