Dandy! I gave some thought to a vacuum leak but they normally cause problems at low speeds, mainly a high idle and hesitation when accelerating.
If that line runs to the right rear of the transmission, that is connected to the "vacuum modulator valve". That is what sets the shift points. Under acceleration you will have lower vacuum. That tells the transmission to delay the up-shifts until you reach a higher speed. When you're slowing down with a closed throttle, the vacuum will be high and the down-shifts will occur at much lower speeds.
If you ever run into that hose sliding off repeatedly, suspect the modulator valve is leaking. The transmission fluid will rot the rubber hoses and make them mushy.
Chrysler only used a linkage to adjust the throttle valve in the transmission. That also adjusted line pressure so under harder acceleration the clutch packs had more pressure applying them to reduce slippage and make a firmer shift. Ford used some of each. I'm not a Ford expert but I know you have to look to see if they use a modulator valve or a linkage.
Very happy you solved this and was not a serious problem.
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Wednesday, April 24th, 2013 AT 9:39 PM