What was found
AIRCRAFT GROUNDED. APPROX 31000-31700 W/ AUTOPILOT ENGAGED, AUTOPILOT STARTED A DECENT. WE HAD ALTITUDE DISAGREE AND AIRSPEED DISAGREE. COMPLIED W/QRH FOR ALTITUDE UNRELIABLE AIRSPEED DISAGREE 80 KT DIFFERENCE. INSPECTED LT & RT PITOT AND STATIC DRAINS FOR MOISTURE AND BLOCKAGE, IAW AMM 34-11-02. NO MOISTURE AND BLOCKAGE NOTED. PERFORMED LT & RT PITOT AND STATIC LEAK CHECKS, IAW B737 AMM 34-11-00 & 34-11-01. NO DECREASE IN ALTITUDE OR AIRSPEED IN 1 MIN, NO DIFFEERENCE IN INDICATION OF LT & RT ALT OR AIRSPEED. AIRCRAFT AT 23000 FT WITH AN IDENTICAL DECREASE OF APPROX 70 FT ON BOTH SIDES, CHECK WITHIN LIMITS. REPLACED RT IRU, IAW B737 AMM 34-21-01. REPLACED RT ADM, IAW B737 AMM 34-24-04. OPS CHECK NORMAL.