What was found
AFTER T/O, HEARD LOUD THUMP DURING GEAR RETRACTION, INDICATIONS NORM. IN FLT W/AP ENGAGED ACFT STARTED PORPOISING. AP WAS DISENGAGED, DIFFICULTY CONTROLLING PITCH ATTITUDE. DIVERTED. ON APPROACH 165 KTS BUFFETING FELT, FLAPS 15, 170 KTS. FERRIED, A COMPLETE VERT STAB & ELEV CHECK INCLUDING CABLES, PULLEYS, BEARINGS, SURFACES & ELECT CONTROL SYS PERFORMED. AUTO PILOT STAB TRIM SERVO CONNECTOR (D381) PIN NR 3 FOUND LOOSE & WORN THRU INSULATION. REPLACED CONNECTOR, STAB TRIM BRAKE, AUTO PILOT STAB TRIM SERVO MOTOR, FLAPS UP LIMIT SWITCH (S245), STAB TRIM CUTOUT SWITCH (S272) & STAB ELEC ACT LIMIT & TAKEOFF WARNING SWITCH (S546). LOUD THUMP DETERMINED TO BE NOSE GEAR LOCK ACTUATOR, WHICH WAS REPLACED.