Jackomo

Hey guys, So I have an R31 Wagon with an RB20neo conversion. The engines runs fine, however I am getting a hesitation/flat spot when I hit 3500rpm on full throttle, as if the engine is on 50% power?. I've changed the fuel filter and everything was clean. But I'm trying to crack down if anyone has had this problem before? Reason I came up with could be: Spark plugs? AFM? Fuel pump? (Currently stock Rb30 fuel pump) Coil packs? I'm not too sure which. any help would be much appreciated. Thanks