What was found
AIRCRAFT WAS GROUNDED. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO CLT. THE CAPTAIN REPORTED ON ROTATION THAT THE AC WAS SLUGGISH AND SLOW TO ACCELERATE. DURING CLIMBOUT, THE AIRCRAFT FLIGHT DIRECTOR WAS PITCHING INTO VLS AND CONFIRMED SPEED WAS MANAGED, PM CONFIRMED IT WAS MANAGED, AND THE FMA READ MANAGED. THE SPEED BUG WAS WHERE IT SHOULD HAVE BEEN, BUT THE FLIGHT DIRECTOR WAS PITCHING UP A SLOWING INTO THE VLS. CAPT SELECTED SPEED AND ROLLED IT UP TO 250 KTS. AC WAS STILL SLOW TO RESPOND AND CAPT TURNED OFF ATS WITH AUTO THRUST PB AND MANUALLY TOOK CONTROL, THE FLIGHT CREW INITIALLY HAD TO PUSH THE TLA ABOVE THE CLIMB DETENT WHEN AIRCRAFT TRENDED SLOW AS THE AIRCRAFT CLIMBED. ONCE LEVEL AT 6000 MSL THE FLIGHT CREW ATTEMPTED TO RE-ESTABLISH THE AUTO THRUST. AFTER RESELECTING ATH PB ON AND PLACING TLAS INTO CLIMB DETENT, AND MANAGING SPEED, THE SPEED ACCELERATED RAPIDLY ABOVE 250. CAPT USED ATH TLA BELOW THE CLIMB DETENT TO MAINTAIN SPEED. PF CYCLED THE FD SWITCHED AND ATH PB AGAIN. SPEED REMAINED STABLE AFTER PLACING THE ATH TLAS BACK INTO THE CLIMB DETENT. CAPT PUSHED IT PAST THE CLB NOTCH, AND BACK INTO FLX. CAPT THEN SELECTED AUTOPILOT. AIRCRAFT REMAINED STABLE. THE AIRCRAFT LANDED SAFELY AT CLT WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED FAC2 PER AMM 22-66-34 (AALA202606089397) AND THE FCU PER AMM 22-81-12 (AALA202606085312). A SATISFACTORY OPERATIONAL CHECK WAS ACCOMPLISHED.