Tranny Shudder 127k Miles

Hello all! So I F'd up and bought a 2006 V6 4.0 2WD Double Cab taco and apparently totally missed the "rumble strip" tranny from 3-4 and 4-5 gear during my test driving. It has 127k-ish miles and has 2-3 records on carfax of the tranny being "checked" but no specific call outs of fluid changes, and I know not all shops report work so for all I know, it's been 127k of unchanged tranny fluid.

I had Toyota do a drain/fill (not a flush) so the 4 quarts and they added BG ATC Plus (transmission conditioner). I did not mention the shudder issue or any concerns and they just added the trans conditioner without me asking so I can assume they either do this for older/high mileage vehicles or they figured it "needed it" after seeing the fluid that came out.

It was shuttering like it was driving over rumble strip on 2 tires from 3-4th gear and 4-5 gear. More so the 3-4 gear which I see in these forums is common unfortunately.

After the change, I drove from 0-50 mph with some uphill and stop/go for 40 miles and about 1.5 hours of driving hoping the issue would go away. It's still there, but it doesn't happen as often or as badly now it seems. It certainly APPEARS to be improving, and I assume if this was 127k original fluid that it will take more miles/time for this to really clear up.

It now mostly only happens on a pretty steep incline, and the 3-4 isn't as improved as the 4-5 gear shifting, 4-5 seems better for sure.

My question is, should I only go a couple hundred/thousand and then have another 4 quarts changed out? Should I do this 3-4 times (idc about the cost as a tranny is a hell of a lot more!) just to be safe and help purge it without a full "flush" as I don't want to risk killing the thing. Or should I get a full flush after 2-4 drain/fill 4 quart changes knowing most of the sludge/crud should be out by then? I want to play this as safe as possible and keep this truck as long as possible as it has a brand new frame and low milage for a taco.

 

I also want to point out that I know similar variations of this have been asked, but no one comes to conclusive solutions (which is understandable) and I want some reassurance this will either continue to run 300k+ miles like it is, or if I need to do something else. I've seen people say they bought a $500 tuner on Amazon and that helped, something about Toyota programming the shifting/trans relation weird? I know very little about transmissions clearly, thanks!

 

I have this currently on my 09. My mechanic got in and literally said "oooooohhh". Called it "torque converter chuggle". Mine happens going into 5th real bad and got stuck the other day on highway. Advice was a new trans as there are no doubt pieces moving about.
227k miles, issue started around 199k

 

I should have came back to this a long time ago, but a fluid swap + lubeguard and shudder fix solved the issue, about 20k miles later it hasn't done it since.