As a test, I’m uploading a 3GB file here on 1.8.4.
It uploads without errors as expected, and the file size and contents match in the library (I’m running md5sum on them both to verify).
What settings exactly have you got in your config.env for:
CMS_PHP_POST_MAX_SIZE
CMS_PHP_UPLOAD_MAX_FILESIZE
CMS_PHP_MAX_EXECUTION_TIME