I've run into a couple of problems and was wondering if anyone could point me in the right direction. First of all, a quick run down of the motor and turbo setup. The bottom end is a gsr block with AEBS sleeves, CP 84.5mm pistons, Pauter rods, and stock LS crank. The head is cnc ported (can't remember who), Ferrera valvetrain, stock ITR cams, Edelbrock manifold, 76mm tb, 1600 cc injectors, and a Weldon FPR. The manifold was fabricated out of 2" od tubing with .09" wall. I don't know the exact specs of the turbo but it's somewhere between a GT40 and GT42. The turbine housing has a 1.22 ar and is divided. The wastegates are twin Turbosmart 38mm Ultra-gates. Boost is controlled by a NLR AMS-1000.

Now for the problems. This same motor and turbo EXCEPT the turbo manifold in a different car made roughly around 780 whp @ 35psi. Now it's only making 680~690whp at the same boost in a different car with a different manifold. Not too bad? Here's the problem. The current combination can spool up the turbo about a 1000 rpm sooner than the old one. You wouldn't think that's a problem but the power is short up top. Any guesses as to why?

The other problem that I'm running into is that the boost will stabilize from 5700 to around 7300rpm then it starts to creep up until redline. Is it possible that the two 38mm wastegates don't flow enough or does the manifold have something to do with it?

Could the two problems be linked to eachother? Our guess is that the manifold has something to do with it. What I'm looking for is an explanation to why the manifold is causing these things to happen rather than changing the it without ever know what was wrong.

Here's a picture of my current setup:

 

that is an ACCEL DFI distributer ?