87' 5KQT turbo overpressure

[Matthew Poynter <mpoynter@zoo.uvm.edu>]

Folks,

I realize this has likely been dealt with before so even some directions
to the appropriate source for the following information would be greatly
appreciated.

My newly-aquired 1987 5KQT is consistantly activating the turbo
overpressure switch (fuel cutoff) when accelerating under part or full
throttle conditions.  It accelerates very nicely up until it hits the
overpressure switch and it is possible to accelerate without causing it
to trigger but I must be careful.  At an indicated 1.5 bar pressure
reading from the dash guage it appears to trigger which sounds normal.
I can't seem to locate and vac/pressure leaks but it has been cold
outside and I may not have been as thorough as I should be.  Any clues
as to where to check first?

My sincerest thanks,

Matt Poynter