i was driving my turbo 2000 tonight its running light mods, exhaust intercooler, uprated fuel pump and its been mapped, as i was coming on boost the car seem to hit a big flat spot at 3-4 thousand revs like hitting a brick wall it would clear but it was doing it in every gear . i havnt changed the plugs in a while so im not sure if this could be a problem. can anyone give me some advice as i want to sort it as soon as poss

 

car is also running simtek ecu so no maf.