My daughters 95 JGC has ~200k miles on it. It started to shudder when down shifting I believe it is O/D to drive but it could be drive to 2nd. I pulled the transmission pan off to replace the filter and found what I consider a lot of filings. I cleaned up the pan, changed the filter and filled it up with ATF+4. Went for a ride and it was still doing the same thing. I found when I was driving it, it wouldn't down shift when I kicked the accelerator down. When slowing down to stop, the transmission would down shift but then the shuddering would start. If I put it in neutral the shuddering stops. If I down shift manually from OD - drive to 2nd it doesn't shudder. I have a bad feeling the transmission is in need of a rebuild.

One other thing I noticed, I tried turning off O/D while I was driving it at 55 and it didn't downshift. So I'm not sure if O/D isn't working or if the O/D switch isn't working.

200k is a good life for an automatic. Sounds like you have a couple of issues. I'll guess that the shutter is actually the lockup converter...those are more prone to shutter than the clutches and bands inside the trans.