[77newell]

In addition to what Gordon said, while the 30 conductor plug is pulled, checking the voltage on the pin that sets the cruise control to the "on" setting. Since you first reported the problem getting worse while driving it may be worthwhile to leave it on for a while and continue to check the voltage. I would also shake the wiring near the MPU and the ECU while checking that voltage. If indeed the problem gets worse as you drive I would suspect heat as contributing to the problem, the the failures are entirely random while driving then I would suspect vibration as the instigator. The part subject to the most change due to heat would be near the ECU rather than the MPU.

The thing I find most puzzling is your statement that the cruise light got brighter momentarily when the cruise burped. That would indicate a momentary increase in voltage to the light. I doubt the internal relay in the ECU would alter its behavior at this moment so the internal supply voltage to the relay must change at that moment, which leads me to wonder if the electrical supply to the ECU is somehow compromised, or, heaven forbid, the ECU itself has an internal problem.