Renault laguna 1.9dci jerking at 60mph

Hello,

I have a 2000 renault laguna 1.9dci and its developed this strange problem, when i'm cruising on the motorway in 5th at around 60mph i can feel the car jerking, if i go past this speed or under, its fine think it does the same in 3rd as well.

any ideas please ?

thanks in advance.

Renault laguna 1.9dci jerking at 60mph