Been having a problem with my 99 gs300 not shifting like it should. Taken it to 3 different Lexus dealerships and they all have told me all diff things, changs transmission(done it) sensors(done it) had the transmission computer box replaced. They told me their getting a code now thats C0200 (RT FT Speed Sensor) would this sensor have anything to do with the shifting in my car? He told me when he was driving the car with the computer hooked to it it reed that the car was going 65 but on going like 40mph. When it rides it rides but it will pop out sometime when i get about 50mph and when i stop at a light it want go into that second gear sometimes. Sometimes cutting the car off and back on helps. My VSC off light is on but its been on for years after i had my ball joints fixed.

 

https://www.clublexus.com/forums/performance-186/ <———— Gen 2 performance section is that way.
Hope you get it fixed, but it may take a transmission specialist to diagnose the correct fix.

 

I took it to 2 transmission specialist and they were the ones who told me that nothing was wrong with the transmission, they was lost with this one.

 

Then they weren't specialists or couldn't be bothered to figure out what may've been causing the issue.