What was found
DURING CLIMB FROM 6000' TO FL390 DUCT PRESSURE SPLIT BY UP TO 25-30PSI. LEFT DUCT VARIED FROM 62 TO 75PSI, RIGHT DUCT AT 40-45PSI. WHEN LEVEL AT 390 AND POWER REMOVED TO CRZ , DUCT PRESSURES NORMALIZED. GROUNDED - YES. PERFORMED B737-900 MM TASK 36-11-00-700-802, FOUND PRSOV VALVE DID NOT MOVE SMOOTHLY OR RETURN FULLY TO THE CLOSED POSITION. INSTALLED MIG51 TAGS TO BOTH ELEC HYD PUMPS AND FLAP HANDLE. REMOVE & REPLACE PRSOV REF B737-900 AMM TASKS 36-11-04-000-801, TASK 36-11-04-400-801 OPS AND LEAK CK OK. REMOVED MIG-51'S FROM COCKPIT - OK FOR SERVICE.