On the RR5700's you can play around with P9, P10, P11, and P14. These all have to do with the speed on the accessory hydraulics. 1 being the slowest and 9 being the fastest. If you have any mono mast reach trucks (RMD6000 or RM6000) there are performance settings where you can set it to automatically cushion.
Otherwise I would check your poly stops. If they keep slamming the reach assembly back into the mast your poly stops may be worn out causing nothing to soften the blow. These are located on the carriage assembly on the bottom. They typically are white or yellow with a hole in the middle for the bolt.
Unfortunately the best option is operator training if neither of those options above work.