just check the dv, 99% of the time, its the dv.
Had the new d revision one fitted 2 months ago, so would be surprised if it's that.
If your idiling ok then its maybe not a leak in the piping. You would see your boost going up just beyond the 11psi then dropping back down to the 11psi. Rememer this happening on one of my old cars.
Iain
Been out blasting about a bit today and noticed the boost is dropping off just before 4000revs, so that would sugest to me that it's leaking when under load.