http://www.youtube.com/watch?v=NkV2PNuUr54
Notice it shifts at about 45 MPH and the engine seems like it powers down, at this point it has trouble picking up speed but it does pick it up, about 0:11 mark is when I left foot off of gas and then give it gas again at 0:14 mark, then let up on it again at 0:16 mark.
Changed spark plugs but cannot figure out the problem.