Not to bring up a dead thread, but I'm having this exact issue..
When we first got the Suburban 2 weeks ago CC worked fine.
On trip to PA (~500 miles) it mostly worked most of the time, but would go out on large bumps or steep hills.
Toward the end of the trip it stopped responding altogether.
On the way home it worked perfectly until the last 30 min or so when it stopped altogether.
Today on the way to work it worked perfectly.
On the way home it didn't work at all.
Everything else on the multifunction works perfectly.
I think brake lights work fine.
CC module seems to be all that's left. Any ideas?