This is the first iteration of Premiere Pro using GPU acceleration using OpenCL, and there is still room for improvement. We're working with our partners to make the OpenCL acceleration better. I can't make specific promises about whether and when updates might be released, but I can say that you should stay tuned for news.
What GPU are you using?
Tell us more about your hardware, your source media, and how you're using it.
See this page for resources about making Premiere Pro work faster:
http://adobe.ly/eV2zE7
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Todd Kopriva, Adobe Systems Incorporated
product manager, professional video software
After Effects team blog
Premiere Pro team blog
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