Ford Repair: 67 Mustang with C4 Automatic, screw hooks, throttle linkage

Question
I have a 67 Mustang with a 289 mated to a C4 automatic transmission.  I swapped my heads out for a better set and now my transmission will not engage into 3rd gear.  I have never had the kickdown linkage from the trasmission to the throttle linkage connected because I don't know how the cable attaches.  The transmission ran perfect until I parked it to swap the heads and since the first test drive it hasn't completely engaged into third gear.  I feels like the trans slips and goes back into second and then slips again and labors the motor rather severely (almost to the point of turning off).  I checked the linkage arm on the transmission to make sure it wasn't stuck in the passing gear position and it is not (I thought we might of hit it with the headers putting those back in).  The car drives absolutely fine in 1st and 2nd gear though.  Do you know what my problem may be?

Answer
Brett,

The first problem is that you must have the kickdown linkage connected. If you have the cable type kickdown linkage, have someone push down the gas pedal while you are looking under the hood and you will see the throttle linkage down near the transmission. The end of the kickdown linkage, with the holes in it) goes on the throttle linkage. The other end of the kickdown linkage, that has the nut and screw, hooks down onto the transmission kickdown lever. That is probably your problem, if not...one of your bands probably needs to be adjusted. If this does not work or you need further help,  please contact me and I will try to assist you further. Hope that this helps and good luck.

Ken