Editing Issues with Adobe Premiere Pro CS4 on Windows 7 Professional

​I was in the market for a PC that could handle editing HD videos for my YouTube channel. I came across Dell's Precision workstations because they advertised heavily on their integration with Adobe productions. I've owned the Adobe Master suite CS4 collection for some time now and use Adobe Premiere for editing my videos. For the most part it's been working great.​

​However, I recently purchased a Nikon D5500 camera to shoot videos and have had trouble editing my footage when importing into premiere. The timeline is very choppy and laggy which is suprising giving hte fact I had my computer designed for this very purpose. I always configure my sequences to match video footage to ensure smooth editing and the problems still persists.​

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​One work around I found was importing these files into Any Video Converter and converting them to mp4's and then bringing them into premiere. However this method is time consuming and i would like to be able to just shoot from my camera and import them directly into premiere pro cs4. If anyone had any advice or knowledge please let me know as it would be greatly appreciated. Below is my hardware / software information:​

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​COMPUTER​

​Dell Precision Tower 7910​

​Windows 7 Professional English 64bit​

​Intel Xeon Processor E5-2603 v3 (6C, 15MB Cache, 1.6GHz)​

​16GB (4x4GB) 2133MHz DDR4 RDIMM ECC​

​Nvidia Quadro K620 2GB​

​1TB 3.5inch Serial ATA (7,200 Rpm) Hard Drive,FPWS​

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​CAMERA​

​NIKON D5500​

​Frame Rates / Sizes: 1920 x 1080, 60p (progressive)/50p/30p/25p/24p, ★high/normal 1280 x 720, 60p/50p, ★high/normal 640 x 424, 30p/25p, ★high/normal​

​File Format .MOV​

​Video Compression: H.264/MPEG-4 Advanced Video Coding​

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​SOFTWARE​

​Adobe Premiere CS4 w/ 4.2.0 update ​