Cruise control problems...

That "berger button" you checked on the clutch pedal...there is also one on the brake pedal. Make sure both are tight and functioning properly. That is a big problem with that specific truck (I too have experienced it).
Some times it will work, but then a bump would knock the truck out of cruise. The button should be depressed with pedals in 'non-use' position...then when you step on the clutch or brake, the button should be completely extended.

 

In front of the arm that connects the foot pad to the firewall or bottom of the dash plate (if I remember right).

Should look like this:

 

Inspect the wire harness that runs from the right side firewall, along the top the engine, to the ECM. This harness has your cruise control wiring in it. This harness likes to rub through on the firewall, rocker cover, or the brackets along the left side of the engine.

 

Very good point!

 

There's easy fix. What I did is duct taped piece of cardboard to the clutch pedal at the place where pedal touches the switch, and cruise control and engine brake are both back to normal. I have Volvo. Its been a while since original post, but I hope it will help someone else.

 

Driver side cab cowel air manifold with air pressure switches should be one with a yellow stripe for ECM service brake signal, these fail and Ecm disengages cruise thinking the brake pedal is depress.