Here lately my 2006 F-150 has had a shutter/binding around 1200 RPMs. This happens only when you give it a little gas. It hasn't happened when I have been in it hard. It is such a hard jolt that my wife feels it in the passenger seat. It has around 87K on it and I have just had the transmission serviced. It was doing it before I had it serviced and it did it a few times yesterday. ANybody ever experienced this?