1996 century trans problem

Driving from a stop the trans shift very fast to o/d and the engine boggs down but it does not happen all the time

The PCM shifts the car depending on sensors and vehicle speed.

Perhaps your TPS has failures and needs replacing. Throttle Position Sensor
VSS thinks your going a different speed. Vehicle Speed Sensor
MAP sensor failing. Manifild Atmos Pressure


Good Luck

Welcome to AF.

It would help to post the mileage. When was the last tranny service. ATF and screen filter?

Are you saying it shifts directly to 4th (OD) skipping 1, 2, 3 or is it just hard shifting or shifting too soon? What does it do when you manually shift gears?

The 4T60E autotransaxle has a vacuum modulator that controls line pressure through the valve body. So check the vacuum line connection to it or a possible ruptured diaphragm.

When an engine is under a light load or no load, high vacuum acts on the modulator to allow the transmission to shift early and soft. As the engine load increases, vacuum is low which causing the transmission to shift later and more firmly.

I have 104,000 miles on it,was last serviced 60,000.The trans does go thru all the shift point and when the trans acts up it goes thru the shift points very fast and goes right to od.I am not getting any check engine lights .

That is enough mileage to possibly warrant a pan drop service. I would not do a flush with your mileage. Also, check out the vacuum modulator. You could get the car scanned with a trans capable scanner to see if any tranny related DTC codes are stored. Not all trigger a SES/CEL light but are stored for retrieval.