98 Blazer rpm fluctuation

The rpms fluctuate about 100 rpms under normal driving. It sounds as if the torque converter is engaging and disengaging. Does this sound like the TC is bad? How can I check? Any other ideas of what could cause this?

Thanks.

Welcome to AF
Lock up changes rpm 300 or more rpm.
How are you checking it?
Can you feel it or just see it on the tach?
Does it do it in all gears?

You can see it on the tach, hear a clunking noise and feel it. It is not a loud noise or a hard jolt. If you aren't paying attention, you probably wouldn't hear or feel it. We first noticed it in the tach. It seems to only do it in 3rd gear and drive, but once you get to about 60mph it doesn't do it anymore. Really didn't do anything other than drive it to test.

Thanks.

You can see it on the tach, hear a clunking noise and feel it. It is not a loud noise or a hard jolt. If you aren't paying attention, you probably wouldn't hear or feel it. We first noticed it in the tach. It seems to only do it in 3rd gear and drive, but once you get to about 60mph it doesn't do it anymore. Really didn't do anything other than drive it to test.

Thanks.

I would get it on a good engine/transmission capable scanner and see what is loing on.
On a good scanner you can watch lockup and slipage and rpms.
if a problem there should be codes set.
Is check engine light on?
Post back any code no.