I'm rolling on 265/75/16's (31.5") and I pull about 2500-2600 rpm at 100km. From memory, stock wheels pull up around the 3k rpm mark. But it's been a long time since I've had stock sized wheels on my rig, so I've no idea really.
And for a 2.5t lump of steel, mines got a few ponies under the hood when I put the foot down.
The challenges is (to me at least) taking something and mouldin git into what I want it to be, it's taken a lot of time (and money) to get my truck upto this point, and all I have left is an intercooler and to wind the boost up. (maybe even look at an aftermarket turbo down the track)
As for your problems mate... I'd be looking at your turbo (being a Chinese job, that's quite likely. Also look at you EGR and intake manifold. I'd almost be willing to put money on the fact your intake is all kinds of choked up.
Also, getting some reconned injectors might be a good idea as well. And as has been said before, of you were looking for power, then buying a non-crd powered truck, is the furtherest from it your could've got.