I had a pair of KAD32's for years and know them pretty well. Before doing anything else I would check the boost to see if the turbo is producing the boost needed and that you haven't got a boost leak in the inlet manifold system. Does the engine black smoke at 2800 or is it running clean? Checking the boost should be only a one hour job so a cheap way to eliminate a number of the most likely issues. Unless your turbo guy put a new exhaust housing on the turbo, 'servicing' it won't fix the most common issue with those turbos which is the exhaust housing rusting away and the clearances between the tips of the vane and the housing getting too big and leaking out the exhaust pressure. One other quick test to try would be to unplug the wire that goes to the supercharger clutch (it is the one that goes into the front of the supercharger usually has a connector you can unplug at the front of the engine) and then run the engine to see what rpms you get at WOT when you go for a test drive. That will give some indication about the turbo boost as the engine should still run up to full rpms without the supercharger.
The injector pump could need servicing and could be your problem, but with such low hours it seems less likely. There is a common issue with air leaks in the low pressure (primer) pump that could be part of your problem, but again in seems less likely with such low hours. I would do the boost test and/or the supercharger unplug test before doing anything more with the fuel system.