"Personal Overspeed" is set in the menu. It's been a couple of years since I have been in a Mack truck, so I can't recall exactly how to get to the page to change the setting. With that being said, the best I can recall is the steps go something like this....
I believe if you hit the arrow button on the left stalk with the key on, engine off, it brings up the menu screen.
Then scroll down to set-up and hit the arrow button
Then scroll down to driver overspeed alarm and hit the arrow button
then change the speed to what you want the personal overspeed to be set at
It won't over-ride what speed the truck is governed to, but it will change when the personal overspeed warning pops up on the dash screen.