Check your render globals. Under the COMMON tab, make sure that "By Frame" has a 1 in the box. 1 means that every frame will be rendered. A 2 would mean that every other frame would be rendered. A 3 would mean every third frame and so on......

If you are not rendering every frame then that would make the final animation appear to be moving faster.

Edit::
I just had another thought: you said that you have to slow the rendered images down in your editing software to bring them back into sync. I assume this means that you are compositing CGI onto actual video footage?? If so, The problem could be that you have Maya settings set to 24 fps yet your video is 29.97 fps (NTSC). If this is true then the animation will appear one way in Maya then it will appear much faster in your editing program. There will even be a slight difference if you have Maya set to 30 fps. Since 30 fps is not exactly 29.97 fps there will be a sync problem too.

Check it out and post what you find...