Hello Mate,
is the MIL on? I suspect not as you would of mentioned it.
Follow what THOR says and if you get no joy then maybe try a new fuel filter, as enough fuel might be getting through at low revs but not at high revs, which could also indicate an injector.

Another thing you could try, you say your've changed the plugs and HT leads with the same result, so now I would re-gap the plugs smaller, and see if it's any better.
If it's improved somewhat, then you have low voltage at the plugs. (possible coil pack).

Try what THOR suggested then maybe my suggestions.
Best of luck