Revving issue

hi have a 2002 Range Rover td6 if I put my foot flat to the floor it will Rev All the way round to 5000 rpm but if I put my foot half way down and let the revs go up slowly when it gets to just before 4000 rpm it sounds like it's limiting but when putting flat to the floor it will Rev through it? Any ideas? Thanks

If you are only going half way on the pedal, it won't go all the way, by nature of how it works!!