SR20DET BLACKTOP no boost untill 5000 rpm?

hey i just got an 85 200sx, i beleive its doug's old one, sr blacktop swapped in. the guy i got it off bought it with a blown T25 turbo on  it and swapped a T28 onto it. he never put it on the road so it hasnt really been driven. i bought this for a new daily driver and would like to figure out the problem.

here are a list of things done to the motor :
ARP head studs
Cometic metal head gasket (oem bore)
New oem water pump
Nismo colder thermostat
All new steel fuel lines
megan racing stainless steel manifold
megan racing stainless steel elbow
Brian Crower valve springs and titanium retainers
stainless steel braided oil and water lines
30x7.5x3.5 Aluminum bar and plate intercooler
HKS ssqv BOV
circuit sports intake plenum spacer/thermal reducer
AEM tru-boost boost controller
AEM Uego wideband
Exedy Stage 2 clutch
14lbs lightweight chromoly steel flywheel
2.5" Straight exhaust piping, dual tip vibrant black muffler
s13 blacktop rad and shroud
Spiral Cell eliminator battery
Garrett t28 turbo

so it doesnt hit any boost until like 5000rpm, i have not have any time to do much investigating yet, im curious what it could be? im wondering maybe an exhaust leak pre-turbo? or maybe some boost leaks in the intercooler piping.

Im new to the whole sr/ turbo thing and any help would be appreciated!

Sounds like an inline 4 to me! ;)

I would look in to exhaust/intake leaks.

Check timing as well

Check if your wastegate is connected properly. Spark plug gap? +15 BTDC? Spark plug gap? Type & degree of spark plugs? What type of bov? And what is boost at 5000 rpm? 1 psi? 2 psi? 3 psi? 20 psi?