1996 Prk Avenue Transmission Shudder

I have 1 96 PA with th 3.8L engine. When drivng at highway speeds, and most after going down hill and accelerating again, my car "shudders" lilke you have run over something in the road. This lasts for a split second and then returns to normal. I am wondering if I have a transmission problem, torque converter or other problems. It does not do it each and every time, is sporatic in nature, doing it only occasionally

does passing gear work??? if you stomp on it does it "shudder"?
the 4t60e has an issue with the passing gear goin out from what ive heard.
mine had to be rebuilt.

This can be caused by a momentary misfire or the tc can be slipping slightly, a full scan with a trans scanner can usually pick out a trans problem. Sometimes a bottle of Lubegard can help the trans shudder but if something in the trans is failing it won't help.