Throttle Valve = T.V. Basically a valve in the tranny is activated via throttle movement. The more throttle you give your vehicle, the more fluid pressure is applied to the frictions and bands. Also the more throttle you give your vehicle the later the shifts occur. Consequently, in your case, the valve is not being opened enough therefore the shifts occur as if you are driving with a light throotle when in effect you are at full throttle.