my rover 75 is over reving?

i have a rover 75 2002 1800cc petrol just lately the engine seams to over rev it goes up to 2000 to 3000 revs and comes down slow if you change geare and let the cluch out at them revs it juderes you have to let it come down to 1000 before you let the clutch out sometimes itreves right up have cleaned out whith red x but nothing thanks mick.