2008 MUSTANG WITH TREMEC 3650 MANUAL TRANSMISSION. WAS ON HIGHWAY DOWNSHIFTING FROM 5TH INTO 4TH TO PASS ANOTHER CAR WHICH ABRUPTLY ENTERED MY LANE WHEN CAR WENT INTO 2ND, LOCKED REAR END AND SPUN CAR, CAUSING ME TO CRASH ON SIDE OF ROAD. CAR WAS TOTALED, LUCKILY I WAS UNHARMED DUE TO SIDE AIRBAGS. THIS 4TH TO 2ND GEAR LOCKOUT HAS HAPPENED TO ME NUMEROUS TIMES ALTHOUGH AT SURFACE STREET SPEEDS SO WAS ABLE TO RETAIN CONTROL. CA HIGHWAY PARTOL REPORT #9645.