Two problems related to transmission gear slipping have been reported for the 1999 Lexus RX300. The most recently reported issues are listed below.
I was driving on a interstate and the transmission started slipping until it gave out.
Simply driving the transmission started to slip, very quickly (20-30 miles) the transmission was slipping so badly the car had to be put into 2nd gear to get it to the auto repair shop. The car will not drive in drive and can only move forward in the lower automatic gears.