Sounds like it's not getting boost like it should. It's probably blowing some black smoke as well?
It would be worth having a look at the turbo and its controller (the actuator might be vacuum, not sure, and the boost control solenoid has been problematic in the YD25s, don't hear much about the V9X). The turbo might also be failing. Given its location, checking it isn't easy. You need to check the shaft wobble.
An easy way to see if it IS the turbo: find the large hose that goes from the turbocharger to the intercooler at the front. Undo the clamp on one end and pull it off so you can see inside. Wipe a fingertip on the inside wall about 50mm inside the tube. Now examine your fingertip under a strong light source. Are there any sparkly flecks in the oil on your finger? If so, your turbocharger might be ready to cross over into the afterlife.
There are two choices here. A new turbo (that's the usual fix) or a rebuild kit which contains a full set of gaskets and new bearings and seals. The rebuild is obviously cheaper (especially if you're skilled enough to do it yourself) and will work fine as long as the old bearings didn't wear out the hole they were mounted in. If you suspect too much wear, don't risk it. Genuine turbochargers can be bought from Qld for under $1500.
Of course, it might not be the turbo, but check that pipe first we'll go from there.
