Oooooh I think I know what you have there, back in the late seventies or thereabouts some Ford trannies had a modulator valve that had two ports. They were meant to be used with one line going to manifold vacuum and the other to ported vacuum (above the throttle plate). I think the reasoning was it made the trans more responsive to actual load, I do believe the trick is to get a modulator with a single port and swap it out. I think these came on some larger trucks and motorhomes, it reduced hunting shifts where the load could vary widely between full load and none.
For high performance toss it and get the single port modulator and try to get one that has the hollow setscrew in the port, you can crank that screw in or out and raise or lower you shift points (increase firmness too). Any C6 modulator will fit I believe but don't quote me (Ford changes designs as often as I change diapers around here! :p ).
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”
— Han Solo