Need help! Shudder w/ overdrive

[Jpete16]

I have a 97 3.4 automatic 4wd. It has a random shudder that most often spread at 45-60 mph. It had become more frequent lately. I drained my transmission fluid and replaced it with withclean fluid. I have found that when I turn off the overdrive the shudder doesn't happen. I'm curious if this could be something other than a transmission issue? Is there harm running with overdrive off, or just worse gas mileage?

Any help would be great,

Thanks guys

 

[kball]

If the shudder happens under light throttle in overdrive my bet is it's your spark plugs. They are probably worn to the point that it throws the timing off just a hair. This happened to me and many others and changing them got rid of the shudder.

 

[Jpete16]

Thanks I'll give that a shot, it's a lot cheaper than having the transmission serviced.