Are you sure your viewing quality settings aren't set to 480p? When watching the video on YouTube, click towards the bottom of the video so it pops open the controls, click the GEAR icon at the bottom of the video, click QUALITY and change the resolution to the highest available (which will be the highest you uploaded I believe).
If that's set to auto, YouTube chooses which quality to show and I noticed that sometimes it'll randomly choose 480p and I have to change it.
