Why does File Explorer hang frequently in Windows 8?
For me, the Windows Defender is the cause of this Explorer slowdown. Here is what I get when scrolling through the Explorer:
Look if you also have this high CPU usage. if yes, disable Defender and install a different AV tool.
Are the files that you're browsing on a separate hard drive (not your boot drive)? If so, that 5-10 seconds are the drive spinning up and seeking. This is the default behaviour of the power settings in Windows 8.