Transmission Rumble/Stutter

So I am driving a few weeks ago and when I would gradually accelerate the transmission would start this stuttering issue, if I let off the gas or accelerate the problem would go away. Now my transmission has been overheated twice, while in Japan my daughter decided to go mudding and in the process clogged up my radiator with mud, I resolved the issue by servicing the transmission. The next overheating issue is when she drove to upstate New York to get a 4 Wheeler, two welders, sand blasting cabinet and tools from her aunt. Towing the trailer through the mountains once again caused the transmission to overheat in the mountains, being in Virginia the only thing I could think of is getting it home to self diagnose the problem. She drove from PA to VA in D3 averaging 50 mph. Once it was home I put I on the lift and seen where it once again overheated and lost a good amount of transmission fluid. I proceeded to level the 4Runner on my lift, warm the transmission to the proper temp and fill the transmission to the factory specs with Toyota WS transmission fluid. I drove fine for about 5 months then the shuttering started, after researching the issue on YouTube several people suggested this anti-shutter additive. I was skeptical at first but there were numerous reviews so I decided to try it and for $5 buck on Amazon the stuff actually works, after driving several days there has been zero shutter or shifting issues. Just passing on information to help others save time and money.

 

Lubegard Platinum is what I use and it's great. What is the stuff you went with called?

 

Whats the shuddering feel like?

I've started to notice my transmission is 'sluggish' getting into gear, say from Park to Drive, or Reverse to Drive. Seems to shift fine through the gears once driving, just those initial changes are sluggish. I did a fluid flush not that long ago. I'm thinking it may be like an actuator or something.

 

Feels like driving over a long rumble strip in the road, when you let off the gas or accelerate the problem would go away.

 

I’ll look when I get home and check my past order information and report back.

 

I discovered a faulty Flexlock torque converter valve in the tranny valve body as the cause of my shudder/chatter like being on a washboard road. There is a test to confirm the Flexlock system failure -drive around town in S4 ( instead of "D") and see if it does not shudder.
This issue is well known and exists across many Toyota models of vehicles . There are TSB's going back many years.
I saved this screenshot:

 

i was skeptical about Lubegard for my Acura MDX when it started to shudder, Ill be dammed but that stuff worked. I dont know how it works but it did and the shudder stopped. Id give that a try first.

 

It worked in mine too. My sister had this thing before me and told me that it used to shutter at low speeds sometimes. I added some lubeguard and since i've been driving it, its been good to go! Idk what's in that stuff, but it is going in every time I do a drain and refill now

 

It is Lubeguard.

 

To be more precise since Lubeguard is the company and they have more than one product, I believe this is the precise product being used by most for the shudder...

Lubegard 19610 Instant Shudder Fix, Instant Shudder Fix and or Dr. Tranny Instant Torque Converter Shudder Eliminator.

There're at least 3 different packagings of this product it seems and with slightly different labeling, but the actual tube of product in these packings are exactly the same, see photos below all from the same link.

Link

$10 Lubegard 19610 Instant Shudder Fix

https://www.amazon.com/Lubegard-196...3VMRYD06R&gPromoCode=sns_us_en_5_2023Q4&gQT=3

Photo