Quite literally only just saw this mate. I take it you have fitted the 560cc injectors with the Evo 5/6 ECU in place?
You say you just swapped the ECU over with the Evo 4 one and it worked fine, that's not right, because the 4 one is set up for 510cc injectors and the 5/6 ECU is set up for 560cc injectors.
Looking back through my PM's you said you had 560cc's to fit in, are they in the car along side the 5/6 ECU?
Could feel like it's holding back with the 5/6 ECU because the car is being starved of fuel if the injectors are still the stock 4 ones. I never see these visitor messages mate, drop me an e-mail on domain38[at]hotmail[dot]com and I'll give you my proper e-mail addy and phone number so you can get hold of me.