Low turbo boost psi after overhaul - cat c15 2006

Hi everyone. 10000 miles ago I just performed an overhaul on my cat c15 2006 (2005 manufactured) twin turbo at 980k. I used a platinum overhaul kit. After 1000 miles check engine came on and turbo pressure didn't go over 21 psi. Come back to shop, problem found - bad actuator from a dealer, changed. After I back to road I found that my turbo pressure is 28 psi at 1500 rpms at full throttle, what is too low (before that normal was @38 psi) and gage arrow was always shaking +- 2psi. Also when I press the pedal just a little at @10-15 psi boost I was hearing some whistling like an air leak, over 15 - nothing. Months before overhaul installed new itercooler. Week ago at my repair shop checked all system for air leaks - nothing found. Now I just stoped at the truck stop, shut down the engine for 30 min and came back to highway - something changed: my turbo boost doesn't go over 21 psi, gage arrow is stable and no more shaking, and boost pressure grows very slow, after I release gas pedal and then apply it all the way, I counted 7 sec from 0 to 20 psi boost pressure and I can feel that truck loosed power. Thanks ahead for any advices.

 

Last week my mechanic checked for leaks - everything looks good . They blowed air from intercooler entrance towards engine and then from intercooler entrance hose to air filter, all looks good at 100 psi. I'm not sure they checked the bellows. Thanks for suggestions!

 

No, I don't have any codes

 

The clamp looks tight, but I'll test it. The only one thing I didn't test is probably exhaust, but looks like no leaks on pipe. Thanks!