I am telling you right now, dont panic in that regard. It is NOT your TV.
The framerate dip people are noticing has nothing to do with "input lag".
If you have a 1080p TV, you can get the same "smooth look" by just un-checking your 720p option in your PS3 so the PS3 forces it to go in 1080p. Then you will be running at 30FPS and not 60, so it may be less noticeable, or wont even dip at all since it is already less than 60 FPS.
Input lag is something totally different, and has to do with timing or twitch based online games. Nothing to do with framerate dips some are seeing.