thanks for all the input.
just been working on site today and speaking to driver who told me that if you push lever realy hard mast goes down faster!
sure enough when i tried this - full speed
swapped over joysticks between sideshift and lift/lower.
Now lift/lower works perfect.
the joystick that was on lift works sideshift at acceptable speed, possibly starting to fail internally?
anyway I left the levers in swapped over position and all drivers are now happy!!
Just goes to show, sometimes dont think or look too hard at problems, try simple things first