Turbo Looses Boast at 70mph

[Baby Cheeses]

Friend of mine has just bought a W plate 1900 TDI Passat and it has a couple of problems (will sign up but his lap top is also playing up) Anyway apart from the central locking and windows playing up blowing fuses the car runs fine except for one thing you hit 70mph and the turbo appears to loose boast / power, he also tell me the car will red line through the gears and it only when you hit 70mph. My friend bought the car with the ERG valved deleted and it's done 108k miles

Since buying it he has changed the boast valve twice and neither has made any difference, bypassed the boast valve and again no difference and is now stuck in what to do next except get another ERG pipe and refit that.

Any ideas would be very gratefully excepted as my mate says he really likes the car and wants to keep it