What you think are the full resolution videos may be the lower resolution and quality cache video. Even at 1080p, the video files can get quite large, like in 4GB chunks per 15 min @ 1080p. Files that long can take a long time to transfer. Even Quick Transfer is only rated at 80MB/s max.
The SD card would contain your full resolution videos and pictures.
You can turn off video caching under Settings, Camera, Advanced Shooting Settings.
Scroll to the bottom for settings for Cache and max storage used for cache.