I have a ’97 automatic w/175K miles and when cruising at highway speeds and I let off of the accelerator, I get a significant vibration and rumbling noise. The vibration and noise is even more noticeable under hard braking, but doesn’t seem to be directly associated with the braking because if I let up on the brakes it still occurs as the truck slows down. I don’t seem to have any unusual issues when the drivetrain is under load. Does this sound like u-joints? Or torque converter? How would I check the torque converter? Any other ideas?

 

I have the same problem. Basically, this happened when I first bought the truck used (~ 60K miles) and I replaced u-joints in the rear drive shaft and it went away for a while. Now (~112K miles), the vibration is back and is coupled with a shudder on take off. I've been told the shudder is the slip yoke, and it needs greasing. While I have the drive shaft off, I'm going to change both u-joints.

 

U joints and slip yoke needs greased as stated...also check for slop in your rear carrier bearing as well...

 

I edited my post above, as I had misspoke about the location of the slip yoke. Your slip yoke is the yoke on the front of the rear drive shaft. Slides in and out of the back of the tranny. My problems had nothing to do with the front drive shaft, all in the rear.

Anyway, I did the maintenance last night. Greased the slip yoke and changed both rear u-joints and the vibration is gone. Still a slight shudder on take off during a turn or maneuvering but once the grease gets around that should subside also.