How to tell if the turbo has gone out.

I've got a 2014 International Prostar with a Maxxforce engine.

Empty or loaded, I have no power going up hill. Acceleration lugs with weight on the tractor.

I think, in my limited knowledge, it might be a bad turbo.

The shop mechanics said it was a sensor problem with the DEF. Fixing the sensor didn't fix the problem and they insist that it's not the turbo.

Can anyone help me out here?