X15 Jake brake is weak at times

[Yauchout]

without insite its anyone's guess and you would just be throwing parts at it and likely wasting money.. could be a bad tune it could be a failing turbo actuator or it could be as simple as the exhaust gas pressure sensor or many other things ... do your self a favor and get insite. I have seen the exhaust gas pressure sensor cause those problems more often then not. but it is impossible to properly diagnose without access to the live engine data and codes from insite, no one will be able to verify your tune without calterm and a inline adapter. for the money you will waste at a likely poor shop you could own your very own inline adapter from ebay which will likely come with insite on a disk.