Inspect your media files to affirm their frame rates.
GSpot
http://www.headbands.com/gspot/
MediaInfo
http://mediainfo.sourceforge.net/en
If Premiere is incorrectly interpreting your media files,
you can right-click the media file in the project panel and
use 'Interpret Footage' to modify the frame rate.
Note: this must be done before adding the clip to a sequence.