Cadillac Repair: Deville 94 - 4.9l acceleration, transmission shifts, new spark

Question
QUESTION: I have a 94 Deville 4.9 with now 201k miles on it - still runs great but recently I got the following problem.
After shifting in the highest gear (at about 45-55mph) and I accelerate it does not do it properly - then it shifts one gear back (higher rpm) and it works smoothly.
I only have this problem when it engine is warm.
New spark plugs, wires, air filter,...
Your help is greatly appreciated!!!
Wolf
sales@godspeednet.com
www.godspeednet.com

ANSWER: At 45 to 55 mph's the transmission shifts into overdrive and any acceleration such as going up a hill, The overdrive will kick out and you will drop to the next lower gear.

Try this and tell me if it is working properly:

Maintain your speed at all times at 55 mph's and with the AC OFF, use your left foot and slowly start applying the brake pedal with your left foot and feel for a slight bump in the car along with a tachometer drop of about 200. Do NOT increase or decrease the gas peddle and slowly take your foot off of the brake pedal and you should feel another slight bump in the car with an increase of 200 on the tachometer.

Let me know.

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

QUESTION: WOW that was very quick - thanks a lot!
I tried your suggestion but could not feel any bump...
I am not sure what you meant with "a tachometer drop of about 200".

ANSWER: A drop in engine rpm's.

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

QUESTION: Got it but I can't tell because I have the digital panel - can't see any rpm at all.
Thanks again for your quick response!

Answer
Try this test a couple of times, It works best when going up a slight incline. The KEY to the test is to NOT move the gas pedal AT ALL when slightly applying the brake with your left foot just enough to light the stop lights.

If you cannot feel the slight bump in the trans then it is not going into overdrive and You will need simple Electrical schematics, Test procedures and picture locations of the components within the system that is causing you problems of which can't be done on this website which only allows one picture. I do not have a website so you will have to e-mail: onlineautohelp@msn.com in order to obtain the information.