Classic/Antique Car Repair: 1989 mercury cougar tranny, mercury cougar, ford garage

Question
QUESTION: My mercury is awesome for the most part. (Let me start there.) However, I have become increasingly worried about a particular problem that I feel might be transmition related. In drive my car has developed a SLIGHT stuttering between gears. My big concern is that when I go into overdrive I lose power at about 45mph. (I assume this to be where 4th gear kicks in.) Now the fluid has been changed but not the filter yet. I wanted to get some advise before I started tearing things apart you know what I mean? So what do you think sir?
         -Neil

ANSWER: The first thing that i would do before getting to the transmission is the secondary side, high tension, of the ignition system. The load on the engine is very high during these upshifts and a spark plug that will misfire under load will make the shudder event that many have mistaken for a transmission problem. Spark plugs, wires, and coil are the suspected culprits. If this does not work let me know and we will go from there.
Brad

---------- FOLLOW-UP ----------

QUESTION: You were indeed correct about the shuddering. (thank you much!). Still have the issue of shifting up in overdrive. I just lose power at 45-50 m.p.h. I have no more problems on the lower gears and in drive. what do you think?

Answer
Ok, the first thing that comes to mind for this problem is the fuel filter. If that has been replaced and is ok then I would locate a shop or some one with a computer scan tool to check out the computer readings. Even if the orange check engine light is not on it does not mean that one or some of the sensors could be out of range enough to make the car act funny. When the person running the scanner checks it out make sure that person does more with the scan tool that just check for codes. There are operational checks that can be done with the scan tool. Even if you have to pay the Ford garage their over priced fee it is still cheaper that throwing parts at the car to try to find the problem. Stay away from the chains like Pep Boys and such. If this does not work let me know and we will go from there.
Brad