Yep, I know what you're talking about with the choking thing.
How did you introduce the Gentle Leader to your dog? Mine... doesn't *like* it, per se. I mean, he'd certainly rather not have it on, but he mostly tolerates it, though he does go into occasional fits where he puts his front paws on it and lets everyone know that he wants it off. But if I have the lead on his collar and he's pulling, he goes into the choking fits.
You might want to look at the thread stapled to the top of the forum about introducing the Gentle Leader to your pup. I always made my dog sit and let me put it on, and then gave him a treat once it was on. Like I said, he'd much rather not have it on, but he'll sit and let me put it on, and he'll walk with it.
You might try re-introducing the gentle leader with a new approach, or you might try the gentle leader harness, which I know many here have had good luck with.
There are also methods people here have used with simply the flat buckle collar, using a clicker and treats, and a method where you either stop or change directions whenever the dog is pulling. Those are worth researching further, though I know I had problems trying that simply from the.... I look crazy walking around the neighborhood changing directions every two steps, and just standing still in the middle of the road with a dog choking himself on the leash hahaha.
Good luck!