Cadillac Repair: 84 Eldorado Transmission doesnt shift, eldorado biarritz, engine speed

Question
I have a 84 Eldorado Biarritz. The high speed doesn't shift anymore. (I don't know if it is the 3rd or the 4th speed).
I changed the transmission with one bought at the wreckyard and still it doesn't shift.

What else could that be ?

Answer
I have to know if it is 3rd or 4th.

Can you feel the transmission shift 2 times when you start out from a stop ?

If you can then you have 1st, 2nd and 3rd. 4th won't come in until abot 52 mph.

If you maintain a speed of 60 mph with your right foot and lightly apply the brake with your left foot while still maintaining your speed you should feel a little bump and the engine speed should increase. When you let OFF the brake pedal in a second or two you should feel another slight bump and a decrease in engine speed. This will verify that you have 4th gear.