Is your case airflow good? If so, you may have a faulty card.
Well actually, this might be it? Because I was recently given a new case, and I did notice that it makes my PCI-express slot sit a lot lower, so my card is a lot closer to the bottom of the case than it use to be....... But I don't think I can really remedy this without getting a new case ugh.
Not sure if it downclocks or not