1HZ fuel problem - motor dies when reaching max revs

Hi,
I have a 1HZ '97 80 series with a DTS turbo fitted. 5 months ago the motor started using more fuel than normal and seemed to be down on power about 20%. All filters have been changed several times since this problem surfaced and the fuel filter inspected. Tanks and lines flushed. Nothing unusual in the fuel filter, in fact, mechanic said it was very clean at last check. He has done a "hot set", (not entirely sure what is involved there) and that improved response around town slightly, but on the highway it is a slug, I now drop to 85kph up a particular hill whereas it used to hold 98kph.
I used to be able to count on 900ks minimum total distance from both standard fuel tanks before empty no matter what type of driving - highway, offroad or outback touring on dirt tracks (CSR and the like). Now, the best I can get is 750ks no matter how easy I take it. No additional mods or gear has been added to the vehicle for several years, always serviced, doesn't use oil or loose water, still builds turbo boost as it always has. The only other problem is when I need max revs (e.g. 2nd gear - foot flat to the boards) the motor will suddenly die back to idle, a huge cloud of grey smoke will come out of the exhaust and it will take 20 seconds or so to return to normal. Engine has done almost 300k ks.
Could the fuel pump need an overhaul? As this is very expensive, it's not something that I want to do if it is not the problem.
Any ideas??
Tony