like edward says there could be a limit switch on the boom not working correctly or a wiring issue in that circuit. Also the limit switch on the swing limit, usually when swing is more than 10deg past center it will slow down the speed.
The boom has to be straight in center of travel line, fully lowered and retracted completely to get full speeds.

you also want to double check the controller in the basket and make sure the pot is giving its full range to the controller. Sometimes these pots go bad or the linkage to it gets loose and allows the gear on the pot to slip.

as for the settings the controller uses it would be nice to know the drive controller this unit uses. If your looking to find one at grove you probably wont since the manlift division no longer exists. You'll have to find a dealership that used to carry grove and might still sell parts that MAY have a manual for it, that's a longshot though.

one more thing
check the switches on the basket control panel and see if it has a switch for torque speeds used for driving on inclines. one setting allows for fast speeds on level ground and the other setting gives it more drive torque but is a bit slower.

a few things to check for while scratchin yer head ;o)