Loss of engine power

Hello, has the check engine light been on at all? and no other warning lights on? This may be a catalytic converter failure, when the converter fails and melts down due to a rich running condition, it will clog up the exhaust. This prevents the engine from being able to take any fresh air in. The first thing you should have done is have the Engine Computer scanned for diagnostic trouble codes, your local parts store should be able to scan it for free and see if there's anything else that might be causing the power loss. A failed sensor can put the car into Limp Mode and that will also prevent the vehicle from going over a certain MPH, but usually it's about 30MPH. If you're able you can take the front Oxygen sensor out and see if you can get the car up past 10MPH, that would allow the exhaust pressure to escape that may be building up.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter