shuddering

I just bought a 2004 TJ x with 158000 miles and minimal mods. I noticed that I get a pretty bad shudder after accelerating and shifting into overdrive, and it's almost always around 1800 rpms. Is this a bad torque converter? I got it scanned and the only code was for an O2 sensor.

Update: Do not buy from the site I listed. I found a bunch of reviews through Google and they are not a good company. My torque converter and tranny has taken a crap on my '03 TJ with the 4.0 & 42RLE. I don't think I'm going to rebuild it, but instead am going to buy one that comes with a...