Ya, adolescent brahmas are usually described using words like stork, giraffe, and dinosaur, so it is probably the teenage gangly phase. Joshua G mentioned TSC's Dumor, they do make a 20 & 24% protein chick starter if you want to up it a little bit.
What is the protein % on what you are feeding? Have they been sick in any way? At that age, besides worms, a low level case of coccidia would be something to think about, even if they haven't been in contact with other chickens. Brahmas do tend to be gangly, not chubby like some breeds, but...