Gluttony could be a man of his word when he wanted. This was one of those times. He fully intended to do what he could to help Lust get out of whatever the hell Sloth had done to her. Life just wasn't the same with her not being... well Lust. He honestly felt Sloth had overstepped his bounds with this one. Making people lazy was one thing but taking over another Sin was just a dick move that pissed Gluttony off.
Although, you wouldn't think that consider the bounce in his step as he made his way up to Greed's apartment. Once there he rang the doorbell over and over until Greed finally answered.