I thought it was hesitation

I suspect you are way in the wrong area. The glaring clues are the 200 rpm increase, and the speeds at which this occurs. This sounds like your torque converter is unlocking. The torque converter sits between the engine and transmission. The engine spins a fan. The fan spins the fluid. The fluid spins another fan that turns the transmission. This all sits inside the torque converter. There is some slippage in there that allows the engine to keep on running when the vehicle is in gear, but not moving, as in when sitting at a stop light. Chrysler invented a lock-up clutch in the mid 1970's to mechanically lock those two fans together for better fuel mileage. Every manufacturer uses a variation of that today. It will only lock up above a certain speed, typically thirty five to forty mph, only when in the highest gears, only when the engine is warmed up, and only when the throttle is held fairly steady at cruising speed. It will also unlock when the brakes are applied, in anticipation of coming to a stop.

To tell if this is what is causing the problem, drive at highway speed with the engine warmed up, hold the accelerator pedal perfectly steady, then with your other foot, briefly tap the brake pedal. You will see engine speed increase about 200 rpm, then drop back down about two or three seconds later.

If the same thing is happening on its own, the two most common causes are the brake light switch is out-of-adjustment and the rattling pedal is turning the "lock-up cancel" signal on momentarily, or there's dirt or a bad connection inside the throttle position sensor. The torque converter will unlock at wide-open-throttle to provide double the torque, and at close-throttle, to allow the engine to slow down while coasting. An intermittently-lost signal from the throttle position sensor can confuse the computer into thinking it should unlock the torque converter. If the brake light switch is suspect, hold it up with your toes to see if the problem stops occurring.

Most of the time this is not a torque converter issue. It is a lock-up clutch control system issue. The lock-up clutch is just following orders. It is those orders that are wrong.

When I experiment with this on my vehicles, I use the Chrysler DRB3 scanner. That shows the "Inputs and Outputs" associated with the lock-up function. It will show if lock-up is "requested" or "denied". In the rare event you see "requested", but it is unlocking at times, that is due to a defective clutch, low fluid level, or the wrong type of transmission fluid was used. It is more likely you will see it switching back and forth between "requested" and "denied", in response to something. You have to watch those inputs to see which one is changing when the unlocking occurs. My scanner will list the brake light switch as "pressed" or "released". If you see it change to "pressed" when you are not pushing the brake pedal, that will tell you which circuit to look at. If you see it switch to "denied" due to low coolant temperature, you might suspect a defective thermostat that is not letting the engine reach normal temperature, or an intermittent coolant temperature sensor. Those sensors have an extremely low failure rate because there is just one component inside it. It is much more common to have corrosion on the connector terminals.

The point is anything is a guess unless you have a scanner to actually see what is changing and what is simply responding to those changes. Be aware too that only a few models are picky about using the correct transmission fluid. The typical symptom when using the wrong fluid is a harsh shudder that can last from a couple of seconds to non-stop just as the speed is reached when lock-up will first occur. The shudder usually goes away at higher speeds, and it will occur again for a few seconds right after tapping and releasing the brake pedal. That shudder is caused by the lock-up clutch grabbing, then slipping, then grabbing again repeatedly. It is being pulsed on and off to create a smooth, gentle engagement, but the wrong additives in the fluid makes it grab too harshly. That gentle pulsing does not occur at higher speeds. At those higher speeds it is allowed to turn on fully in an instant because you will barely feel it.

Let me know what they find.

Thank you. I only know the site owners recently did some work on the donation system. I recently shut down my automotive electrical web site due to the cost going higher and higher every year. Seems everyone in the internet business makes money, ... Except me. I'd like to set it up again on a different hosting site, if I can find one at reasonable cost. Donations are greatly appreciated, but I'm happy to help everyone.

Thanks for the image we have our tech guy working on that now. Can you tell us what device and browser you are using?

Best, Ken

It has been fixed.

Nice work Max !