My truck shudders at low speeds, generally city speeds from 30/35 to around 50/55 MPH. It is not a constant shudder and usually occurs while cruising, not accelerating. It will stop if I ease of the pedal or speed up a tid bit. Most often than not, it will happen in the 30/35 to 40/45 MPH range. I cannot ever tell, but to me, it seems like it happens when it is between shifting or something? A mechanic friend suggested it may have something to do with the torque converter? Although I can pull 'em and put 'em back in. I am not much more than a DIY shadetree mechanic that works on my own. This is irritating as hell.