Could you describe the jerking a little more? Is there a clunking noise coming from the tranny area or even from the engine bay? My car has done this about 4 times in the year and a half that I've owned it, and I believe there's a TSB out on this, not sure if it would apply to your vehicle though. But when I am cruising on the highway and go to drop it into 3rd or 4th I get a nasty jerk, but more like the engine is actually missing, like it just turns off for a split second and fires right back up, and makes me look like a dumbass that can't shift. Anyways, I believe it has to do with little air bubbles gathering in the fuel pump when you're cruising at highway speed and when you drop it that little pocket of air gets sent through so your engine doesn't get any fuel for a split second. I dunno if this is what you're describing, hope it helps though.