I think Lexus is aware of the problem: Here are couple of excerpts from the DOT web site:
www-odi.nhtsa.dot.gov/cars/problems/complain/results.cfm
MANY OWNERS OF 2004 RX330 HAVE REPORTED PROBLEMS WITH THE 5-SPEED AUTOMATIC TRANSMISSION. THERE IS A SUBSTANTIAL "LAG" IN SHIFTING AT LOW SPEEDS AROUND 20 MPH WITH OCCASIONAL REPORTS OF THE CAR REVVING TO "REDLINE" WITHOUT THE TRANSMISSION ENGAGING. THIS RESULTS IN THE VEHIBLE BECOMING IMMOBILE IN INTERSECTIONS OR WHEN EXITING TOOLBOOTHS. THERE IS A SIMILAR PROBLEM AT AROUND 40 MPH. IT HAS HAPPENED TO OUR VEHICLE AT LEAST 6 TIMES, TWO OF WHICH NEARLY RESULTED IN AN ACCIDENT FROM BEING "REAR-ENDED." LEXUS HAS RELEASED A SOFTWARE UPGRADE BUT THIS REPORTEDLY HAS NOT CORRECTED THE PROBLEM. AFTER DENYING THAT THERE WAA A TSB FOR THE PROBLEM, THE DEALER SAID THAT IT COULD NOT "RECOMMEND" THE UPGRADE.
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MY RX330 HAS JUST COME OUT OF THE DEALER SERVICE FOR THE SECOND TIME DUE TO A COMPLETE FAILURE TO DOWNSHIFT WHEN NECESSARY. ESPECIALLY AS I SLOW DOWN TO ABOUT 20 MPH, AND THE TRY TO RE-ACCELERATE, THE RPM'S GO TO 5500 BUT THE VEHICLE DOES NOT MOVE AND THE CLUTCH NEVER ENGAGES. YOU HAVE TO LET OFF THE GAS PEDAL AND LET THE RPM'S COME BACK DOWN AND TRY IT AGAIN. THIS HAS ALMOST GOT ME HIT BY ANOTHER VEHICLE AT LEAST 3 TIMES. ON THE FIRST SERVICE CALL THEY TRIED TO DO A TRANSMISSION "RESET" I HAVE DRIVEN THE VEHICLE 2500 MILES SINCE THEN AND IT MIGHT EVEN BE WORSE. THIS TIME IT WENT TO THE SHOP AND TWO TECHNICIANS, ONE MANAGER, AND ONE CUSTOMER SERVICE REP ALL TOLD ME THAT THEY HAVE BEEN ABLE TO SIMULATE THE PROBLEM ON TEST DRIVES BUT THAT IT IS "NORMAL FOR THIS VEHICLE", HOWEVER, THEY ARE STILL GOING TO REPORT IT TO THE MANUFACTURER. MY RESPONSE IS THAT THIS MAY BE "NORMAL" FOR THIS VEHICLE, BUT IT IS NOT NORMAL FOR "A" VEHICLE. THEY ALL AGREED BUT SAID THAT LEXUS DOES NOT HAVE A FIX. THIS IS CURRENTLY ELEVATED TO THE LEXUS COMPANY CUSTOMER SERVICE AND THEY SAID THEY WOULD GET BACK TO ME. UNTIL THEN I AM STUCK IN A DANGEROUS VEHICLE.