Transmission Sensor Replacement on 1999 Lexus RX300

I am thinking about replacing the transmission sensors myself. Is this a difficult repair? Can the sensors be accessed easily? The reason I am considering this is that the transmission will not shift into overdrive.

Asked by for the 1999 Lexus RX300
It's a good idea to get a repair manual if your going to work on your own vehicle, and it's never been easier or less expensive to get a good one for your vehicle. Try or and you can have one in minutes, for less than $30.00.
Read up on the job you are about to perform, it will show you what special tools you will need and you will be much better prepared to tackle any job on your vehicle. It will also give you diagnostic and troubleshooting info.