06' Aveo Transmission jerks or hesitates intermittent at highway speed only

[Ryanlas]

Hi Aveo people,
I have a 2006 aveo, Auto Trans, that i have been tinkering with. About 135K miles. Engine starts, idles, accelerates, decelerates normal. No codes. It shifts through all 4 gears normally (and torque lock). I recently dumped and refilled the transmission fluid. added a quart of Lucas transmission happy stuff.
When driving between 50 and 60 Mph the transmission will jerk or hesitate slightly, and at random. Its a small jerk. slight loss of power to the wheels for a fraction of a second and then normal.
At lower speeds it runs perfect. also at 60-75 it runs perfect.
Seems that it does it more when going uphill or more engine load is present.
I was thinking TPS sensor or something.. Seems to me that the computer is telling the transmission to misbehave. So i'm inclined to think its some sensor. Torque converter unlocking and relocking at random? what input tells the torque converter to lock?
I have read a ton of forums looking for clues. Nothing definite. some folks think bad ignition coil, plugs or wires. I'm not sure that makes sense. Also no codes to read.
Thanks in advance for any input.
Ryan