fuel, leaning out big time under load
 

I got a walboroo fuel pump and everything works fine my air/fuel gauge shows stoich.
but between 2500 and 3500 rpm it seems like (and the gauge shows) its leaning out big time under load??
everything is in spec car is not boosted or anything and I have a FCD which worked perfectly fine on my old motor.
where to start ?

title updated to have the actual question in it

is it an s5 t2? do you have the rats nest removed?

no not yet
I do however have most of the emissions control valves pluged and air pump removed
why does that make a difference???