Sounds fishy. Sure it's new? Or did he replace the seals, crank the adjustment screw down to remove all the slop, paint it, and charge you for new box?

As ramair68 mentioned, the adjustment is for set up from the factory. You can use it to get rid of a tiny bit of play if the box is slightly worn, but more than that is going to cause binding and really fast wear. From the sounds of it, either the it was set wrong at the factory, or by the rebuilder (if it's a reman), or the shop did a hillbilly rebuild on your old box.