What model of camcorder is each of your videos from and what format and resolution is it?
What are the Project Settings, as listed under Project Settings, under the Edit menu?
You don't say which version of the program you're using, but that could also be relevant. If you're using version 14, do you get the same results if you output using Export & Share/Quick Export?
I am using Adobe Premiere Elements 13.
The clips were shot with a Cannon Rebel T5i DSLR camera at 1920x1080 24fps but the file properties show 1920x1088 23 fps.
I forced the settings DLSR 1080pDLSR 1080p24 when I created the project.
The Project Properties show "frame size" = 1920x1080, "timebase" = 23.976 fps and "display format" 24fps timecode.
I created the AVI file through Publish + Share option then selected Computer. I got similar results with both an AVI and an MPG file.
You don't say which Canon Rebel you're shooting with, but there are several models that shoot in a number for formats.
Can you confirm that your camera is set up to shoot AVC/MTS video and not MJPEG? What the suffixes of your video files?
MTS files should work very well -- but MJPEGs (which can be AVIs or MOVs) can cause lots of strange behavior.
And can you confirm that all footage in your movie came from the same camcorder at the same settings?