Susan, don't get too discouraged. I have similar problems with Bentley. I decided that I was going to take baby steps in trying to resolve the problem. My goal was to be able to walk around our small loop without a huge meltdown. Bentley doesn't lunge after cars, but after people (sometimes), dogs and bikes.
Before setting this goal, I did try using the Gentle Leader. It did keep him from lunging, so it was good in that it kept Bentley safe (he has been able to get out of numerous collars), but I didn't feel like it addressed his issues at all. He still barked, and wanted to lunge, just didn't. It made me feel like I wasn't actually helping him at all, and he was still stressed.
I started taking him out for a few minutes during the day armed with a jar of baby food (we used beef and ham). I would put the food in his face as soon as he saw something. The key is to get him the food before he reacts, which means before his "threshold". Because I know that once he starts lunging, it's too late, I can't calm him or even get his attention. Some days we could barely leave the driveway because something was close. Other days we made it halfway up the road before I decided not to push him too far.
But, I had to stop because of the heat. So, once it cools down, I'm going to get back to it.
All of that to say that I don't have an answer to the problem yet. But I think it's going to take a lot of time and dedication.