Freelander flat/dead spot

Hi all,
My mate has a 52 plate TD4 which has a flat/dead spot at about 70mph in top.

It seems to rev and run up to this point but will intermittently hit a real dead spot. The only way to get aorund it is to lift off and decrease speed and then creep up again?

Any ideas please?
Thanks,
W

Possibly an answer in the sticky at the top of the page!