That could be the valve body.... but it could also be sticky governor, servos or accumulator as well, and possibly broken parts or sealing rings too. So, sticky, especially in the governor, could just be dirt, and I mean dirt thats not likely to make it's way out on a fluid change. '66 is a transition year, and the valve body may work, but if I were you, I'd be prepared for the fact that a valve body may not repair the issue at all. You can certainly pull your valve body apart and look for excess wear and sticky valves, burrs in the bores, etc. and throw it back in too. Let us know what you find once you get in there. HTH, Lefty71