2007 cummins isx low overall boost EXCEPT...

I've got a 2007 cummins isx with overall low boost. Ive been having this truck for 7 years and boost gauge usually reads 30+ while under a load. I noticed for the past week I can only get about 15 psi on my gauge while under a load EXCEPT right after I use my jake brake. For instance, if I'm coming down a slope and use my jake to help slow the truck then once i get back on level ground and can accelerate again, at that moment, I have full boost, 30+ on my gauge, but it only last for 15-20 seconds then its right back to 15psi max. The only other time that i can think of where my boost goes to ALMOST normal is while pulling an empty trailer and I go into 6th gear (i have a 13 speed), at that moment i can get to about 25 on my gauge but it falls back to 15 in about 15-20 seconds.

Is there a connection with the jake and the turbo. and please forgive my ingorance on how a jake brake works. The turbo sounds normal, I've checked all clamps and rubber boots for leaks and can't find any. The turbo is not leaking any fluids. egr has been deleted from ecm

I have no check engine light on, so far I've replaced the turbo actuator and the barometric pressure sensor, under the advice of a local "parts changer" ( i say parts changer because the mechanics here aren't very good at diagnostics). I hate to keep throwing sensors and parts at it without a clear direction and like i said, there is no check engine light.

Should i get my ecm scanned anyway in hopes that there will still be some clue as to where to look? I was thinking maybe someone here has had a similar problems with a similar engine before and could help to lead me in the right direction.

Thanks

 

Found an exhaust leak from one of the exhaust manifold gaskets. Almost a half inch break in the gasket. I hope this is the culprit

 

It’s definitely effecting the drivability, no power while under a load