pete 379 2007 c 15 acert no power low boost low fuel mileage and high temp on pyro

007 pete 379 c 15 acert 475 hp tires 11r 22.5
Serial no mxs596737
Im getting a really poor mileage 4 mpg at best 4.5s
The turbo gauge moves slow towards 35 psi. The pyro
Goes upto 10.5
As soon as I reach a hill or slightly elevated bridge or ramp
The speed drops to 25 to 30 mph.
I got dyno. The top hp came was 309
The dyno guy found exhaust manifold red hot and part of primaryy
Turbo also red hot.
I changed the mufflers as they were clogged to straight muflers.
A little better performance but not a great . The speed dropped to 30. And I had 68000 gross
Weight.
A mech opened the turbos to see if they were bad. The turbos
R in good condition.
Im attching photo of hot exhaust manifold.
Pls help. I have already spent 2500 dollrs and no result.
Thanks

 

Here is the pic

 

Nope. The air filters r good.

 

I got cac test done and for any turbo leakss. These were good.
The shop could nt find any problem with these....

 

Is the wastegate the thing on top of the primary turbo that
Has a hose that goes into the tother turbo...?