video conversion frustration

I have a blu-ray/dvd player that will only play videos with certain codecs...primarily xvid. I have a large video library of avi videos that i am converting /recoding to either mkv or avi but with the xvid codec..i have tried many commercial and free video conversion programs (Aimersoft video converter, E.M. Total Video Converter, FreeMake video converter,handbrake, etc. )
No matter which i use the end result of the converted video has an odd "slow motion" effect or something (hard to describe)...what i mean by that is, for example, that in cases where there would be a scene with some fast motion, that motion is somewhat slowed down in the converted video..no matter what conversion program i try, i get that result..i've tride manually adjusting framerate, and other manual settings...with no luck.
When i use a manual override instead of presets, i use xvid as the codec,, 23.97 as the framerate, and because i'm trying to reduce the quality slightly (so as to reduce the file size to around 700mb or so) i use a video bit rate of 1200kbps..and am always converting the audio to mp3.

anyone have any idea why i keep getting that slow motion effect in the converted videos? I use mediatab and the before and after framerate is the same.

Thanks for any thoughts you might have.
Brian