In most dreams, gender isn't an issue. I'm just "me."
That's funny that you asked this question though, because just last night I had a dream where my trans status did become an issue. I was visiting the house of two brothers I knew as a kid. We lived in a pretty redneck town, but this was further exaggerated in the dream. Bumpy, dirt roads and houses with wooden foundations, raised off the ground. I was my adult, MTF self, and they were still kids. Time was frozen, as it typically is in a memory.
I walked into there house, and there was a macho, mustachioed man named Vulvan -- like a portamento of Vulcan and vulva. He said something like, "Well don't you feel pretty being a little girl?" I told him that I was a grown woman. He then informed me of his intention to stab me. I told him I didn't want to fight, and that I'd just leave. I left the house and got in my car, fearing that any second I could be stabbed to death. I turned the ignition, but the car wouldn't start. I told myself this wasn't a horror movie, and the car started.
So to make a long explanation short, I'm usually MTF in a dream.