Hey! Thanks for your patience - I've been a little busy recently.
What sort of differences are you seeing? Are you able to capture a video of the difference? Are both the GameMaker extension and the Blender script fully up to date (I have done some animation bug fixes somewhat recently)
I might have to peek at the original blend file (privately, of course) if we can't figure it out here so I can check the setup - there are some restrictions with respect to euler rotations, if you are using those at all (only YXZ is allowed)
I'm in the middle of rewriting the export/import and animation system, so this is actually a good time for me to check for fix this sort of issue.