Frankly flushes on high mileage transmission is kiss of death. If a fluid exchange is done (transmission pump is used for the exchange) than it is ok, but a flush machine drives the metal debris thru tranny and probably into the valve body assembly which is death to the transmission. With Loss of overdrive you should be experiencing a check engine light with pending codes. Either that or your check engine light is burned out. Another note sometimes the shift linkage comes loose and the gears are not selected properly. Couple of people over the years have found that. I feel the biggest problem is that the original 1999 tranny had a aluminum planetary gear carrier which eventually wears and than causes the failure of the gears because they drift in the aluminum carrier causing failure. All on this site and the other lexus site agree a flush is not good. I know I tried it once on my RX300 when I loss overdrive and it only got worst.