set up is a stock gsr w/
SC61
inline pro cast manifold
precision intercooler
2.5 charge pipes
aebs intake mani
650 cc injectors
neptune rtp
3 inch downpipe to exhaust

the car still has a/c and p/s and a recirculated dump tube

on 10psi the car only put out 270-275 whp on a dyno dynamics

in an old post people said it could be so here it is so you can see for yourselves

 

My buddy ran all but the same set-up you have their same exact manifold. He didnt recirculate his dump tube at all and on 14lbs he made 355whp. Id say on 10lbs your probably pretty close to being right on the horsepower but id also say that were your dump tube enters back into the down pipe that it is probably robbing you of some power. if you wanna recirculate your dump tube I would have it renter on the next elbow were the exhaust turns to go back under the car....

 

^^ that is true.. but considering it is pointing the same direction as the flow, it wouldnt hurt it that much especially with 3"

What is hurting you is the cast manifold.. they dont flow well above 6k rpms. A mini ram or full ram will make it flow.

Since you have an aftermarket IM, did u get a larger TB and match it? that right there will give you good gains.