Hi! I've taken it upon myself to finish the restoration of a mustang my cousin had bought several years back.

I've just about got the engine all finished up, the last thing to do is figure out the reason for this sudden change;

Now, it has a shift-kit on it, so my cousin says. When I first got it, It would shift hard, and give a nice kick, when shifting to Second Gear, i'd get a bit of a squeel/chirp from the tires from the kick. But suddenly, while driving the hard kick/shift stopped. It shifts very lightly now, and lacks that power.

I'm worried this may have to do with the transmission. So going from a powerful shift to light, almost unnoticeable shifts. Is this an issue that i should be worried about???  

Probably!  

I am in the same boat as you are. I have a '65 289 coupe that I have owned for almost a year. When I first bought it, the transmition was in great shape. It shifted excellent like clockwork at 20mph and 60mph with a strong acceleration in every gear.

In the past week it has started shifting very gingerly, almost hesitantly, from gear to gear and the mph range has changed also. Sometimes it feels as if out of gear just a little too long when shifting.

The only good thing is that it idles a little better and actually stays idling when in gear at a stop. This was an issue i had before where i had to either have one foot on the brake and the other on the gas to keep it running or shift it into neutral at almost every light to keep it running.

If you have experienced these issues or if anyone has any questions/comments, (mechanicalguy48) please let us know.