I looked at this manual.
https://apache.ariens.com/manuals/04276200A_ENG.pdf
Since I didn't have your serial number and Gravely model numbers vary with engine choice, I can't be sure this is the correct manual. This one may be for a different year model and they could have changed some things. However, I can't believe there are no adjustments on a Pro model that they could have at least tinkered with to try and help you. My lower tier HD model has adjustments.
Good luck with them. If all else fails, a call to Ariens/Gravely will most likely put some pressure on the dealer to help, or they may direct you to a more competent dealer.