Struggling with public speaking only in certain situations.. Any Advice?

I posses a great attitude, my speaking skills are up to par and incredibly helpful in selling, convincing, or building great rapport. It's always been one of my best assets. I'm not afraid of expressing my beliefs or concerns in any situation. I make friends easily, open up and smile and express myself. I listen more then I speak, ask questions and overall happy for other peoples success.

However, all this is thrown out the window when I'm speaking with someone who is higher in me in terms of hierarchy, more so in an office environment. Like my managers for instance. It's not that I'm intimidated, but my words lock up on me and I stumble quite often or fidget. When I'm relaxed or tired, I speak so well that I have the room mesmerized.

However, I notice I worry too much, feel guilty and overall worried about what they think of me as I'm speaking to them. I almost believe its a low form of aspergers. I'm all over the place, that I have a hard time focusing on what they're saying or even matching body language.

I have interviews that go better then conversations with my superiors. I'm too anxious and I don't perform well at all.

One of the things I'm trying to improve constantly is my ability to not feel so intimated or worried about what others think of me, especially after I get to know them or work with them.

I was hoping maybe some of you can recommend me some tips, share some advice, books or anything I can learn to help me get over this small bump in social skills.

Keep in mind, with strangers no matter their rank in society it doesn't intimated me, only when I befriend them or work with them, does it interfere. I worry too much, but don't know how to relax and let go and be my True True self.

Cheers,
LivingCali