What was found
THREE MINUTES AFTER TAKEOFF, HAD AN IMBALANCE LIGHT WITH LEFT TANK LOW, AIRCRAFT HANDLING CONFIRMED IMBALANCE. RAN QRH & RETURNED WITH ALL MAINS ON & CROSSFEED CLOSED. DURING RETURN WAS ABLE TO GET WITHIN 500LB BALANCE. AFTER SHUTOFF, NR 1 ON TAXI IN WITH CROSSFEED CLOSED, LEFT TANK QUANTITY INCREASED. ACFT GROUNDED. PERFORMED CROSSFEED VALVE FUNCTIONAL TEST IAW AMM 28-22-00-730-802, AND FQIS BITE IAW FIM 28-41 TASK 801, AND CDS BITE IAW FIM 31-62 TASK 801. NO FAULTS FOUND. PILOT VERIFIED IMBALANCE NEVER EXCEEDED 1000 LBS. ACCOMPLISHED FUEL QUANTITY COMPARISON CHECK OF LT & RT WING TANKS IAW AMM 28-41-00, FOUND TO BE WITHIN LIMITS. SIGNIFICANT SYSTEM GROUND VERIFICATION COMPLETED, NO DEFECTS NOTED.