I too am now experiencing brake shudder at 20k. It happens at higher speeds, think highway with moderate slow downs.
Robert Mauro--Are you serious about a 1,000 mile brake "break in"? I've never heard of such a thing in all my years of driving.... I get bedding the new rotors and pads on high performance sets, but that's usually a series of agressive stops made back to back to back in the first few miles.... 1000 miles......hmmm
Yes, I am very serious. Every set of pads or rotor turning/rotors. These are high performance pads, and #2 of 25 (almost #1) in stopping distance in the class of 25 vehicles. 18 of those vehicles are much smaller 5 seaters. The Ascent crushes most of the competition and is well below the segment average in stopping distance. Same for any current generation Subie (and same reason other models have similar problems when not broken in).
"a series of aggressive stops made back to back to back in the first few miles" seems to ensure your brakes shudder starting at 18K-23K miles. Like my first set (original design, Version A).
My second set (Version B - first revision) was changed 22 miles before a road trip to Florida. They were some of the smoothest braking breaks I've driven on - and they've been through the mountains off road and on road numerous times, and on all sorts of crazy adventures. First half of the trip was 1,200 miles of perfect by the book break-in. Second half was off-roading and fun on a leisurely trip back to NY.
My THIRD set (Version D - third revision) shudders a little. I did NOT break them in properly - my driving nowadays is strictly short distance harsh stop and go.
And, yes, this is in everyone's owner's manual - though there's one confusing section about asking one's dealer (who generally doesn't know) that needs to be removed.
This is DIFFICULT to do. I know. As I said, I failed on pad set #1 and pad set #3 - and I don't have the excuse of not knowing how.

But the difference is STAGGERING.