When driving at 80 MPH the steering wheel vibrates

The most common cause of this is a wheel or tire issue. More then likely the tires need to be balanced. They need to check the road force on the tires as well because if you have a tire that is worn it may balance but when the force of the road is applied to it, the issue presents itself.

Also we need to check the tires for wear. Here is a guide that will help with that:

https://www.2carpros.com/articles/how-car-tires-work

Let's get the tires balanced and make sure they check the wheels for out of round and the road force using a road force balance machine and go from there.

Here is an attachment that shows common tire wear issues.