I have a 1995 Monte Carlo LS with an automatic transmission. It has 125,000 plus miles. At any speed above 50mph it will develop a vibration or slight rumble when adding throttle to accelerate or climb a hill. It sounds and feels like a clutch slipping. There is no indicated surge in RPM.
Transmission fluid is full and clean. Until recently I could shift to "D" drive and the vibrations would go away. There has not been any problems with transmission to this point. (Original owner)

However, there has been problems with electrical connections in other systems. Recently it has had some relays that didn't work due to bad connections. Oxidation and/or corrosion.

I always suspect electrical due to the connection problems. But does this problem sound like it could be an electical problem with the tranny or mechanical inside the case problem?

 

Hi Bakerman, Have your checked your transmission mounts to make sure they are tight ? Check back on your thread later to see what our expert tech member's post/suggest.
Good Luck...

Below search Results:
Shocks

Worn shocks can cause your transmission to vibrate. If you find your transmission and car start to vibrate during travel on uneven or bumpy roads, this is because your shocks no longer operate at peak efficiency. A bad steering stabilizer can cause similar symptoms. This can cause the transmission and the entire car to vibrate during times of extended use. Improper lube levels in the transmission can also cause vibration. U-Joints

Improperly installed or worn-out U-joints can also cause transmission vibration, regardless of speed or road quality. You can tell if your U-joints are bad or incorrectly installed if you hear a thudding sound when the transmission changes gears. The same thudding sound can be heard when suddenly changing speeds. Have a licensed technician change your U-joints regularly. The Exhaust System

One of the most common sources of transmission vibration lies with the exhaust system on your car. Sometimes, replacing your exhaust with one with different specifications than the original factory exhaust system can cause the normal operations the exhaust performs to pile up and send ripples of vibrations through the entire car, all the way to your transmission. A bent exhaust pipe can also do this. If you're going to replace your exhaust system, always make sure the specifications on the new model meet and will work with those required by your make and model of car.

 

Original factory shocks still bounce "good". Ride is no different on rough or smooth pavement. Better than my newer rides.

U-joint klunk non existant.

Original factory exhaust has no kinks and flow is good.

 

Transmission is slipping. Yesterday it missed a shift. Going to the "doctor" next week.