It may be a controller setting issue. I don't use Mach 3 any longer but I do recall it has an exact stop mode and constant velocity mode with some setting for tolerance. Those may not be the names for the setting but they should be something like that. On the Cam side you can set G61 or G64 to control what mode the controller is in. G61 is exact stop and G64 is the constant velicty mode.