Yeah, when I used to make gifs they would do the same thing to me. I only had internet explorer at the time. They looked fine to me but people would complain they were moving too fast and I didn't get it. Then, once I had Firefox, I could see how fast they were really moving. Just change the the frame rate. It's probably set to 4 but by selecting all the frames > right click > image properties, you can change it to whatever you want. 8 is probably the best number.