Is the hash rate that the pool shows you inaccurate, because my hashrate is apparently at 82.9 GHash/s and I haven't overclocked:
{"hashrate1m": "82.9G"

Now 2 minutes later it has dropped to 53.1:
{"hashrate1m": "53.1G"

If the pool (CKPool) hashrate is accurate, clearly the U3 is very unstable.