Limp mode problem TDi

[BargainBucket]

I've got the quite common problem of my passat going into limp mode under load, under 60mph it's fine but anything over and happens. Switching engine off sorts it out until I get to 60 again. Done a search and the main culprits seem to be the MAF and n75 valve, I've change both and the problem is still there.

Any ideas what else I can do next, makes driving the car very annoying!

Cheers