Only thing I can think of is how you might have installed DG.
If you can, save what you have, dump DG, or move it alone to an external drive. Then clear your cache and reduce the amount of saves you have if you have a lot of them.
Then put Skyrim in the external drive. Then put DG in your XBox, then put Skyrim in after it. For some reason, they load better in that sequence (the same with Dragonborn).