1.check the mechanical "Doggie Bones" and cable connections between the :
accelerator pedal and the injection pump.[Lengths and ease of operation(lubrication)]
2.check the mechanical connectios between the cruise control actuator (motor)
and the I.P., the transmission, the accelerator linkage.[Lengths and ease of operation (lubrication)]

There is no direct electrical connection between the cruise system and the EDS
(Electronic Diesel System)[engine computer].

What you describe is that the cruise system is somehow affecting the boost...
Only possible through the "Fuel Rack Position Sensor" getting stronger information from the mechanical connection between the cruise and the I.P ; than the information from the accelerator pedal mechanicals.

The boost is controlled by the EDS through two Vacuum/Electric Transducers.

Look at the Vacuum/Electric mess just in front of the coolant surge/overflow tank(in front of the battery) on the passenger wheelwell.