How to make the rpm to come back down to normal

Hi, my name is Devin. I am an auto repair expert with the Car Genius team here at RepairPal. I'm sorry to hear you're having trouble with your Tahoe. When the RPMs stay high after a thermostat change, it's often due to an air intake or vacuum leak that may have been created during the repair. Ensure all hoses connected to the intake manifold are secured and inspect for any loose or cracked vacuum lines around the throttle body and intake area. Also, ensure the throttle body is clean and operating correctly, as carbon buildup or a sticking throttle plate can sometimes cause high idle. 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!