I have a 90 s13 with a s13 sr20 blacktop. The car ran fine when I got it, pulled the motor and when I dropped it back in it's not running right. All I did while it was out was had the turbo rebuilt (gt2871r) and got a fmic and that is ALL! It has factory sr harness and uprgraded fuel pump as well.
What the car is doing...
Idle is fine, it's not missing but when driving the car is stuuupid slow! Feels like it's being restricted. Right now I'm running open downpipe but with the full exhaust on it feels more restricted (sounds worse than the raspiest honda you could imagine x10).
At wot my boost gauge shows 10 psi (have it tee'd off the Fpr) which I thought was weird because it's got the stock wastegate and I thought it should be 7 psi?? This car ran fine before I pulled it out and I'm stumped... Any ideas??

Did you by chance get your fuel lines backwards? Where is your boost gauge line hooked up? Could you have a boost leak closer to the throttle body but still getting boost at the turbo?

^ what he said. Check the throttle body coupler make sure it is to the line.