HEST light on too often...

[dbl overdrive]

I would verify you have the correct calibration .Also, the most up to date cal as well.
30 psi can be a silent derate and 20 is for sure but you need to be under full load to know.There is a way to monitor silent derate in insite maybe someone here can chime in on that. Boost on a healthy engine will normally be about 38 to 40.
The turbo could be so clogged with soot that it won't allow the vanes to move freely. Have you tested injectors yet? Or cylinder cutout test?