give Buck Henderson a call at backyardtrainingkennels.com He trains many gsp. He is just north of Dallas.
I am biased and have limited exposure to trainers but Buck is great, he started my Vizsla who is going back soon for the full puppy program. Most of the dogs with him when I took my dog were GSP's. Buck's kennel is clean and the dogs are well taken care of and trained. I was extremely grateful for the knowledge he has shared with me as far as training already. I'll continue to spread the good word on Buck every chance I get.