I've had enough of my boss telling me to slow down.

I've had enough of my boss telling me to slow down. I have been a stutterer for as long as I've been able to talk. Some situations it's not a problem, others it is a major problem. I have also managed to hold my job for nearly 20 years and I am a manager at Wendy's. I've always felt like the owner of our franchise didn't care to understand my problem, but I am helpful and do a decent job, so he "puts up with" my speech problem. Lately our company has gone to a customer service first oriented operation. They want us talking to the guests and asking how their food is and whatnot. Basically building a relationship with our customers. This is tough for me with my stuttering, but I do the best I can. Lately though, whenever the owner of the company calls: he talks to me like a robot and says to take a deep breath and calm down and slow down. I've told him that does not help and will only make me more nervous when I'm talking to him, because I know he's expecting me to talk to him like a robot. He continues to do it, and I don't know what else to do.