1995 Mercury Cougar Torque Converter Clutch Shudder Causes?

I am having an intermittent problem that seems like it results in torque converter clutch shudder, based on posts from people with similar problems. It always occurs under the same circumstances - about 1600RPM, under light acceleration, more often when going up a slight incline. If I let up on the gas slightly, then accelerate a little more, it always stops. I can drive the car in a way that minimizes the occurrences, but it is my wife’s daily driver, and she has not yet developed the knack for avoiding it.

This has been happening for quite some time, and seems to be influenced by multiple factors. About a year ago, we did have the transmission fluid changed, which helped reduce the frequency of the shuddering. Not certain, but the change was probably done in the most minimal manner.

Two other times, I found improvement after performing other seemingly unrelated maintenance… once we had a low coolant situation that made the shudder more frequent and severe, especially going uphill. I also noticed a significant reduction in the shudder after replacing my spark plug wires a few months ago.

The car has 168,000 miles on it, and aside from the occasional shuddering, it looks good and runs well. I would like to keep it for another year and 15,000 or so miles.

I would like to believe that if I take it in to have the pan dropped and have it fully drained, flushed, and refilled with the recommended Mercon fluid, it will work perfectly. Well worth $200 or so. However, I’m concerned that doing this could make the situation worse, requiring more serious transmission rebuilding, and/or that it will have no effect whatsoever since the problem is really caused by something else.

What sensors, solenoids, or vacuum components are involved in the lockup system? Since it only happens under gentle throttle pressure, I wonder if vacuum could be involved. I would expect that if it were purely related to the fluid that it would happen under more circumstances.

Thanks for any insight.