C-15 not giving full boost

What does your temp gauge show? I just dealt with similar situation with a bad connection on the coolant temp sensor. All the usual checks found nothing. No codes, but when taking it for a ride, I noticed it had a status flag for "cold run mode" and the temp gauge was below 100. It was stalling around 30 psi of boost. With a infrared temp gun it was really 190 at the T-stat housing. New sensor and harness end got the temp gauge working and we were able to get 40 psi on a small grade empty. Driver says it's back up to 45-50 loaded now.

 

You need a laptop with Cat ET for that. I'm not saying that it's your issue, it's just a similar issue that I ran into for the 1st time recently that made me scratch my head for a bit. It should not be in cold mode at 150*, so I'd look elsewhere.

May not be an option for you, but my next step would be to have someone else drive while I use Cat ET to monitor all sensors and look for something out of the ordinary. Then I'd run the injector and intake actuator tests. It'll be a process of elimination starting with the easiest things first.

 

On your truck, the temp gauge runs off the data link, so the ECM and the gauge are getting the signal from the same sensor. If you suspect that the gauge is not accurate, then look into it. But if the gauge is accurately reading 150* , the ECM is seeing 150* as well.

In my case, the gauge was bottomed out below 100* at all times (the ECM showed 75* on Cat ET), even though the engine was 190*.

 

I've got same thing in the morning turbo wont spool and after I hit 150 degrees and above it will break loose. I was told its a cold mode.