This sounds like a hardware problem. The playback engine in Premiere has been very, very fast since CS5, so it is unlikely to be a software problem. The data rate for 1440p video at 47fps is going to be astonishingly high (170MB/sec once decoded, for comparison, 1080p 24fps is just under 50MB/sec) and extremely demanding on your system. Based on your system specs, it probably isn't a processing or memory problem, particularly if you have CUDA enabled, however you may be running in to a bandwidth problem loading off your hard-disk or loading in to memory (depending on your memory speed).
It also may be an issue with the format of the video you are using. Not all video formats are designed for random access. Even with a very powerful computer, if the file format you are working with requires rendering out multiple frames from the latest key frame every time that you move your preview, you will hammer your computer far harder. (In the worst case, you end up having to load over a dozen frames of video to get one frame.)
It also wouldn't hurt to double check if anything is bottle necking by looking at Task Manager when you are previewing video. Does memory utilization or CPU get high? I expect it will be hard disk access (which won't peak the CPU or memory utilization) but it doesn't hurt to double check.
