What was found
AIR TURNBACK, FLT CONTROL WARNING. ON CLIMBOUT FROM PHX, MASTER CAUTION LIGHT AND FLIGHT CONTROL ANNUNCIATOR ILLUMINATED FEEL DIFF PRESS, WHEN MASTER CAUTION WAS RESET FEEL DIFF PRESS REMAINED ON. REMOVED AND REPLACED A AND B SYS HYD RETURN FILTERS (NO VISUAL SIGN OF CONTAMINATION), LEAK CHECK GOOD. PERFORMED PITOT LEAK TEST AND TEST OF FEEL FORCE SYS, OPS CK GOOD. RECOMMENDATION: REMAIN OPEN, MONITOR.