Unfortunately it sounds a lot like "yikes" to me. The turbodiesels do have a higher flow requirement than the non-turbodiesels. The pumps were totally redesigned and chain driven on the turbos and the almost always have higher pressure at idle than do the V8s.
They all should instantly peg the gauge when reved. I would be sure about the electrical on the gauge and If the pressures are correct I would live with it till you see a change or send in your oil for testing to see if you are into the brass portion of any bearing.
Bosch Master, ASE Master, L1
33 years MB technician