Sigma vs Sony 18-250

I bought the Sigma 18-250 after being convinced that it will have a better IQ as well as being quieter for video. I was looking forward to it being better than the Sony 18-250 which I had already stowed away ready to be shipped back.

However, the first few shots with the Sigma is disappointing; twice it could not focus at all and when it did, it was far slower than the Sony. (I had SS turned off) I thought a few pics were OOF and when I uploaded the pics to the computer, I find that most of them were indeed OOF. I was testing it at the 250mm end where I expected the IQ and lens stabilization to be the most effective.

I wonder if my copy is not the latest stock with A55/A33 compatibility? It does seem to focus again when I turned if off and on. Also, the box it came in does not mention a US address anywhere for warranty or service purposes. Do I have a grey market sample?

Perhaps I've gotten a good copy of the Sony lens? The A55 with the Sigma is noticeably heavier and bigger which made me appreciate the Sony 18-250 quite a bit more.