This was the update for the check valve issue.
Check Valve Failure In Priority Valve
D5M (6GN, 3CR, 7LR, 5ES, 6AS),
D6M (3WN, 4JN, 5NR, 6LR, 4HS) TRACK-TYPE TRACTORS
Some reports have been received that the 9U-8076 Check Valve has failed in some priority valves. When the valve fails, oil is allowed to flow from the high pressure (controls) side to the low pressure (converter) side of the system. This scenario results in low system pressure available to the transmission and brake control valves. The general symptom has been that the brakes drag whenever the priority valve is at low pressure.
During proper operation, the priority valve raises the low pressure side to high pressure in order to supplement high pressure pump flow under the following conditions:
1. Cold oil (below 40 °C (104.0 °F)
2. Engine speed below 1300 RPM with the parking brake OFF
3. During a shift (speed or direction)
If the machine operates correctly when the priority valve is at high pressure, but operates poorly when the priority valve is at low pressure, then a failed check valve is the most likely cause of the problem. Inspect the 9U-8076 Check Valve within the priority valve. Replace the valve, as required.