2001 Toyota Land Cruiser

IN THE PAST FEW WEEKS I HAVE ENCOUNTERED A SITUATION WHICH I FEEL IS QUITE DANGEROUS. THE FOLLOWING HAS HAPPENED ON FOUR OCCASIONS WHILE ON HIGHWAYS AND INTERSTATES. WHAT OCCURS IS THAT I WILL BE DRIVING ON A HIGHWAY AT ABOUT 65-70 MILES/HR WHEN SUDDENLY THE TRANSMISSION SHIFTS INTO A MUCH LOWER GEAR. I AM NOT SURE WHICH GEAR IT IS, BUT IT IS INTO A VERY LOW GEAR. TWO THINGS HAPPEN. THE CAR SUDDENLY SLOWS DOWN RAPIDLY WITHOUT THE BRAKE LIGHTS COMING ON WHICH CAUSES THE CAR BEHIND ME TO COME CLOSE TO REAR-ENDING ME. BUT A WORSE SITUATION IS THAT THE SUDDEN DROP INTO A LOW GEAR CAUSES THE CAR TO SUDDENLY DODGE TO THE RIGHT - I ASSUME BECAUSE OF THE ENORMOUS TORQUE GENERATED BY THIS SHIFT THAT OCCURS WITHOUT THE ENGINE SLOWING DOWN FIRST. THIS HAS OCCURRED TWICE ON INTERSTATES AND TWICE ON TWO LANE HIGHWAYS, ALWAYS AT HIGH SPEEDS BETWEEN 65 AND 70 MPH. WHEN THIS HAPPENED LAST WEEK ON A TWO LANE HIGHWAY, THE CAR DODGED TO THE RIGHT. TO KEEP FROM GOING DOWN AN EMBANKMENT I STEERED HARD TO THE LEFT AND OVER STEERED A LITTLE, ALMOST HITTING A MOTORCYCLE IN THE ONCOMING LANE. ON TWO OF THE OCCASIONS, ABOUT A HALF-HOUR BEFORE THE CAR DID THIS, I WAS DRIVING WITH THE CRUISE CONTROL ON AT ABOUT 65 MPH AND THE CRUISE CONTROL WENT OFF BY ITSELF FOR NO REASON. I TOOK THE CAR TO A AAA DESIGNATED TRANSMISSION SHOP YESTERDAY. THEY TOOK IT FOR A TEST DRIVE AND RAN A SCAN BUT FOUND NOTHING. THEY THOUGHT IT WOULD BE IN THE CRUISE CONTROL OR ELECTRONICS OR SENSORS.*JB