I strongly suggest you start by getting your hands on the chart for your engine/trans like oldDave57 shows in his reply, then do a normal driving test comparing your experience with the specs given in the chart. If your transmission is shifting from intermediate to third gear at a speed within the range given in the chart, I would NOT mess with the passing gear link. If it does not shift within the range given in the chart, proceed to re-adjust the passing gear link per the directions given in the Ford-O-Matic shop manual (or whatever trans that is).
Now road test again and it should shift at the proper speed. Now test the passing gear and see if it downshifts when you stomp on the gas pedal.
Don't go willy-nilly screwing around with the passing gear adjustment without any reference to what is right. You can easily get the adjustment so far off that it can damage the transmission !