After driving my 1998 C5 for about 30 miles the cruise control will disengage. Some times it will let me resume but then disengage again. The car will start surging slightly at this point. I checked the DIC but no errors are displayed in history or current. If I let the car sit for an hour I can use the cruise for about 30 miles again. I have heard that there may have been an update done to the PCM for a 1998 C5s and also that there was a common problem with the brake switch. I have made an appointment to bring the car in for service but I don't really want a run around. Has anyone come across this problem?