I have my TP running very rich high in the revs, i replaced the oxygen sensor because the ecu had the error code for it. i also replaced the water temp sensor for the ecu for preventative matenence.

The ecu hover still reports a oxygen sensor error? and it still pours out black smoke after about 4000rpm

I tried the way my gregorys manual explained to reset the ecu. but without even starting the engine after resetting it the ecu still reports a oxygen sensor error. i dont think it is resetting properly

try disconnecting the battery overnight, this sometimes helps completly clear the error codes. Most of the time a few minutes is fine but overnight will definatly do it.
The o2 sensor will not be regarded by the ecu at the rev range you are talking about, check your fuel pressure, injector flow and to a leak down test, check your dist, the shafts in them get worn and they give bad readings.
Hope this gives you a couple ideas