Garmin GSC 10 Speed & Cadence Sensor Problems

I posted this over at the MotionBased forums too, but since I know the BT crowd is the best of the bunch, I wanted to post here to see if anyone has had similar issues.

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Hey all, having a problem with my GSC 10, and wondering if anyone has any tips before I just order a new one.  It worked great about the first 30 days or so, but a couple weeks back, near the end of a ride, it started flaking out by auto-pausing and auto-resuming at random.  Now, whenever I use it, it reports speeds much much higher than I'm traveling (in some cases, faster than I could pedal downhill), so I'm not getting accurate speed or distance from my unit.  At times it will register 0mph while I'm moving, then jump back up to the "too-high" speed.  The cadence portion seems to still work fine.

I'm pairing it with a Garmin Forerunner 405, and the unit itself is working great - no problems on the run, and if I disable the speed/cadence sensor pairing, it works perfectly on the bike too.  I've tried replacing the battery in the GSC 10, moving the bike mount forward and back to see if that was an issue, removed and replaced the magnet on the spoke (and even the one on the crank arm for good measure), and double checked all the spacings to ensure I was within 5mm of the sensor and the magnet, even hard reset the 405 just in case it was the unit.  Nothing seems to work.

Anyone else had similar issues and, if so, how did you fix them?  I don't mind ordering another unit, just hate to toss $60 if I don't have to.  Thanks!

Edited to add:  I've also tried both Auto-Calibrating my wheel size and manually calibrating it in the 405 itself (using 2096 or 2097 as my wheel size when I do it manually, since I'm on a 700x23 wheel), shows bad readings in either case.  When I let it auto-calibrate though, it gives me a wheel size that is too small, in the 1800's or low 1900's.