If you get "higher" amperage steppers they will work, just at the set amperage of the driver. Maybe the steppers are fine and you need to adjust the driver settings or the controller settings (or its a mechanical issue with the machine. tight bearings, alignment etc). I'd work through the system before replacing anything and track down the exact cause of the issue. What do you mean by "not working well" steppers either work or don't work? usually.. Peter