Why does my 2006 Lexus rx400h not shift gears over 40mph and revvs high?

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. So sorry to hear you're having trouble with your vehicle. If your Lexus doesn't want to go past 40-50 mph, it's very possible it is in "limp mode." This means the vehicle has detected an error in a system that could damage powertrain components, so it is restricting output. Although less likely, failed internal transmission components are also a possibility. I would recommend getting the issue diagnosed as soon as possible to prevent any further damage. If you need more advice, have any other questions about your vehicle, or would like to get connected to a RepairPal Certified shop near you, we have you covered. Give us a call at 877-913-1554, and we will happily help you out!