if the truck is moving when the deadman pedal is depressed this means the travel pot is out of adjustment or is going bad.
9 times out of 10 its hotspots in the pot wiper causing voltage fluctuations causing the truck to think the handle is in a direction and causes the truck to start moving even though the handle is in neutral position.

you can go into the TMM through the display control and check this by running an A04 test to check the voltage to the travel pot for variations....
an ideal setting for neutral position is 2.0v - 3.0v
full forks first direction should read 2.75v - 4.75v
full tractor first direction should read 0.5v - 1.75v

as for setting the pot, yes there is a tab on the potentiometer housing but i generally wind up bending that tab back to allow for some adjustment by turning the body of the pot till i achieve the desired voltage reading in neutral which i generally try to set to 2.5v. Once you tighten down the lock jam nut on the pot it wont move. Of course you can try to loosen the setscrew on the gear and get something inside where the gear is and turn the pot shaft but there is no throughhole in the directional control casing to put a screwdriver so thats sorta hard to accomplish. Its easier to just bend the tab back and adjust it the way i suggested.

Unless you have been in one of these systems before it is rather intimidating to navigate through it to find what you need and its not something i will explain here. So if you have not done this before i would suggest calling a cat tech (or a tech that is familiar with this truck) to come do it for you. Giving out passwords or passing manuals around is not a good idea.