First check for errors in the ECU, all sensors can be checked on lose contacts or shortcuts this way, this can easily be done with a light bulb, if this is ok check the mechanical condition of the engine with a compression test, if this ok you check the plugs and leads, beware, if a plug sparks, it doesnot mean it sparks under pressure in the cilinder, if you are not sure, replace it, check fuel filter, air filter and fuel pressure.
Check the injectors on leaking, you have to activate the fuel pump with an extra wire to do this test, then take the injector out.
The ECU does not use the lambda sonde on full throttle so that is not likely to be the problem.
I think your engine is running rich, if you don't feel hesitations on full throttle but you have power loss and no mechanical problems, then i think that is the problem.
One possible cause is the coolant temperature sensor, this also creates hesitations on part throttle, a corroded connector is often the error.
A simple test to see if the engine is running rich is to drive it full throttle for 3 minutes, then cutoff ignition right away, stop and check if the plugs are black.
There can also be a "learning" problem in the ECU caused by for example an intake air leak or faulty lambda sensor. If you find such a problem you can reset the ECU by simply take off a batterie cable for a couple of seconds.