What was found
FLIGHT DIVERTED. CLIMBING THROUGH FL 280 IN CLIMB, IRS MODE NOTICED SPEED BUG MOVE UNCOMMANDED TO 65 KTS. F/O PUSHED IAS/MACH REF. BUTTON TO MACH AND ROTATED AIRSPEED BUG TO .74. THERE WAS NO CHANGE IN PITCH. ACFT/ FLIGHT GUIDANCE OPERATED NORMAL, FOR REMAINDER TO FLT. PRIOR TO INCIDENT, CLIMBING IN IAS MODE AT 290 KIAS. NO SIGNIFICANT TURBULENCE. DIVERTED TO PDX FOR REAPIRS. LANDING UNEVENTFUL. C/W SL-22-006F, DOWNLOADED MDC IAW TASK 45-45-00-970-815-A01 AND FDR IAW TC R313101. PERFORMED OP'S TEST OF FCP IAW TC R221101, ALL CHECKS GOOD. ACFT CONTINUES CAT III, PLACARD READS CAT III. RETURNED TO SERVICE.