Can you tell us the truck details?
Also are you trying to slow down the overall top speed or just the initial creep? As creep speed setting is function 2.
If any of these can give you the correct settings for the truck and then can make adjustments where required. Setting 1 is called MPH scaling dont know if that has anything to do with it, you also have setting 3 which is controlled accelaration etc.. As for after setting it you say it reverts back to 0 setting 12, this could be down to a controller fault possibly as in the past we have had EV100 lx cards which required settings changed in order to work, however after disconnecting the handset the setting would revert back to original, and in that instant it appeared to be a problem with the card. Setting 13 is also related to speed limit, how about changing truck mode? Either way if you can get us the truck model may be able to get settings.