Royce,

Check hydraulic fluid condition along with filter. Turn steer wheel full right and hold for 10 seconds while engine is running. Do the same for full left. Test steering. There is a priority valve in the system that may start sticking. When the steering fades or stops working, does raising the RPMs on the engine help? If so suspect pump or steer valve. You can check secondary pump pressure at hydraulic tilt valve. Should read about 2300 pounds. Good Luck