can you explain in more detail what you mean by setting 'turtle speed' ?

these trucks donot have any definitive buttons persay to set slow 'turtle' speed

it is controlled either by mode settings in the controller via operator selection (if it has a premium display), generally there are usually 4 preset modes with mode1 being the slowest and mode 4 being the fastest, modes 2 and 3 of course are inbetween and these mode changes also effect the lift speeds using a predetermined setting. Also a limit switch in the mast when it reaches a predetermined height the high speed is cut back.
If the truck does not have a premium display and controller then the truck has just a standard speed control setting with no operator options.

the mode settings can be altered by accessing the controller via the ondash display or using a laptop or handset and setting custom settings usually.