I belive Gaara's powers came from the Shukaku sealed inside him. There is a reason why his father decided to seal it in him, and why the Akatsuki members want it so much. Like Naruto, Gaara's power source comes from the demon sealed within him. Of course, Gaara might still know all the jutsus he mastered previously, but now he may not have the level of chakra required to execute them.