RE: Cruise control intermittent problem
You might try adding an accumulator to the vacuum line, a vacuum reservoir
so to speak.  I ordered on from Whitney, local FLAPS didn't stock them.  It
didn't help with the old system but works fine with the new Audivox CCS100
that I had installed last Spring.  Audiovox suggests the vacuum reservoir
for 4 cy engines.
BTW, the Audiovox does not use a vacuum switch on the brake pedal
eliminating that source of problems.