Exhaust brake

[Chamberpains]

On my cm870 it would easily hit 25-28 psi @1550rpm+ on a steep hill. My cm871 is way lower @ 18-22 psi @ 1550 rpm+. Both of them were properly tuned by Mommaburt from the forum. I'd say your low with 18 psi on your cm870.

What psi are you getting under a hard pull? Have you checked to make sure you have no leaks in the air supply to the turbo actuator? Do you have full smooth range of movement from the VG ring in the turbo?