power falling off

well since i did my turbo swap ive been noticing the the car pulls ridiculously hard up to 8psi (max boost is set at 11psi) then the power just seems like it starts falling off and i cant figure out why, the boost doesnt drop off but the power does and AFRs are between 10.1-11.2 at full boost and wot. so i was hopping someone here has any suggestions
mod list
7mgte swap
w58 swap
fmic
2.5inch ic pipes
safc
3inch exhaust pipe turbo back
snow performance water/meth kit running boost juice
eboost 2 ebc
turbosmart bov
aem wide band
swapped in 3.91 with lsd
3 core radiator
egr delete
evap canister deleted
fuel pump 12v relay mod
maft (original)
Pulsation damper delete
wh1c turbo
ffim
100shot wet nitrous kit
electric fans
 
the afrs by 5psi are in the 10s and by full boost its reading 10.0 (thats as low as my wideband reads)and as for boost leak, i guess its possible but it happens at 8 psi and the boost is still going up could a boost leak cause that? i thought as long as the boost was still climbing the power should too right?