Always shifted fine but today it will only shift into low gear

More than likely, we have the transmission wearing out and it is putting metal and clutch material into the pan and that is getting into the valve body.

Basically, we need to start with checking the fluid and seeing if it is full and in good condition.

https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid

Next, we need to drop the pan and inspect for metal.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

Once we know this information we will know if just flushing the fluid will work or if we are going to have to reinstall the pan and check the pressure in the unit.

If the fluid is full and in good condition, then we need to jump straight to checking the pressure so let's run through this info and see what we find to determine next steps.

Thanks