You need to encode the original files to an intermediate format like DNxHD or Cineform. Then import those and edit the encoded files but once you are done editing, change the converted folder name and then tell premiere to look for the files in the folder where the unconverted files are. You need to make sure that the converted and original files all have the same name and file extension for this to work,.
Essentially what happens is that Premiere cannot handle the original gopro footage smoothly no matter what computer you have. The format is terrible for editing, so once you convert you will have a smooth preview so you know what is happening. Then when you want to render the edit you swap the folders so that the original and highest quality video clips from the GoPro are rendered in place of the compressed clips that you edited with. Works great.