What does it cost to replace a transmission in a Toyota Highlander

My first question would be: why are you assuming the automatic transmission needs to be replaced? There are more than one possible cause for your problem. I would recommend having some testing performed. If it turns out the transmission needs to be replaced, where the testing is performed can give you a price for repair and give you options. If the problem only began once a fluid and filter service was performed, it seems to me that there's an internal hydraulic issue that is not resolvable without transmission teardown and rebuild. Automatic transmissions that act like this, temperature sensitive, have internal issues. I would recommend seeing a specialist near you. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops