Issues with driving faster than five MPH, transmission?

The description unfortunately sounds like the CVT has failed internally and the converter isn't allowing the engine to gain rpms as it should. The only real repair is replacing the transmission. For this you need to remove the complete engine and transmission unit out through the bottom of the vehicle, then split the CVT from the engine once it is out. The images attached are the removal steps to get it out. The images just save a lot of typing. Once out you could have it rebuilt or get a remanufactured unit that can be installed without waiting for yours.