Feels a bit flat/low on power between 3k and 4k

[sammyhale22]

My car feels a bit flat from 3k-4krpm if i put my foot down, 4k onwards its like a rocket though. I`m sure its just started doing it. What could this be a sign of?

 

[shadowsun]

Is the engine warm because when cold they're sluggish. Also, what fuel are you using? V Power makes mine much more responsive.

 

[sammyhale22]

Yeh its when its warm too, i use V power all the time. I dunno if my mods make any difference, I have recently installed the Espace airbox with an ITG element and i have a big CAF coming off it. I am running Henks latest ECU calibration file. The only things i have really modified is the airbox and just henks updated file. I`ve also fitted some new plugs, the proper NGK ones because i thought it might be a spark problem.
I read it could be a lambda problem too but rstuner doesnt report any faults.