I replaced the transmission in my 2002 Lexus RX 300 about one month ago. The mechanics reprogrammed my ECU immediately, and they advised me to replace my ECU with a new one, because with the old ECU I will have problems with gears 2 and 3, and my transmission could break again. They also said there may be surges while driving. Is that proper advice? Do I need to replace my old ECU?
Something on the board has either died, or no longer functions properly. If its ECU related and been told to replace ALWAYS replace it straight away, I wouldn't risk driving the car as well so maybe tow it or if its still there just get it. Or buy an aftermarket ECU, but then you will have to get it retuned but you will get better gains out of it.
But overall replace it!