My 2013 Rx350 starting having transmission issues March 2024. I purchased the vehicle with 104K miles in 2022 and never changed the transmission oil. In March 2024 I had the transmission filter and oil changed after a few weeks of shuttering in 1st/2nd gear. The shuttering stopped and vehicle drove like normal for 7 months. The shuttering came back in October along with infrequent rattling noise from the transmission area during acceleration. The vehicle also hard shifts and lags when shifting between 1st and second gear. I had the tranny oil changed last month and It didn’t make a difference. Has anyone had this problem?

 

Who performed this transmission work, and what specific ATF was used?

 

I am not sure about Toyota transmissions, but BMW trans will act strange after a fluid change. BMW's trans "adapt". These trans are used by many auto manufacturer's. When you change this particular trans (ZF) fluid, you reset the adaptations. But even so, often times the trans will act squirelly for a few miles.

Make sure who ever is changing your fluid knows how to do it. Toyota has a very specific procedure to get the correct amount of fluid in there.

Couple more things to consider
https://www.toyotanation.com/threads...alled.1581202/
https://gearstar.com/how-transmissio...le-reset-works
https://www.foxwelldiag.com/blogs/ca...aptation-reset

 

I have never heard of a need for the U660e to adapt after a fluid change. Nothing electrical was touched. That Toyota Camry SE link above has a different transmission, the 8 speed.

It is likely that the trans solenoids may be worn out, or the fluid is low, or it is time to replace it. You may want to have a shop check for stored codes. See the list below of potential causes.

It may be that the cure is worse than the disease. Meaning that you may be able to drive it for years with the transmission acting like this, or it may crap out next month, but the cost to replace it will not change. We are talking a couple of thousand dollars if lucky.
When it dies the most economical repair is to find a good used transmission. There are a lot of used U660e transmission out there as it was used in millions of Toyota and Lexus vehicles over the last 15 years.

Sometimes replacing the solenoids helps, but unless doing it yourself, the cost can be prohibitive for a repair that is a gamble, as it may be other worn components and all are expensive.

​​​​​​Potential reasons for rough shifting in a U660E transmission:
Low or dirty transmission fluid:
Insufficient or contaminated fluid can cause the gears to not engage smoothly, leading to rough shifting, particularly in the lower gears.
Worn clutch plates:
Over time, the friction material on the clutch plates can wear down, causing them to grab unevenly and result in a harsh shift.
Faulty shift solenoids:
These electrical components control the transmission's gear changes, and a malfunctioning solenoid can lead to delayed or abrupt shifts.
Worn synchronizers:
The synchronizers help match the gear speeds before engagement, and if they are worn, the transition between gears, especially 1st and 2nd, can be rough.
Case wear:
The U660E transmission is known to have issues with case wear, particularly around the main gear train bearing supports, which can contribute to shifting problems

 

It sounds like it may just be a bad transmission that needs an rebuild or replacement. I suggest taking your transmission to a trusted highly rated transmission repair shop and let then perform a proper diagnostic on it.

Any answer on this forum is just guess work from members that means well, but are not transmission specialist and even then the unit must be properly inspected in person to see what the actually problem is.

I changed my transmission fluid and did not have any issues after the fluid change. I used Valvoline MAX Life high mileage transmission fluid.

 

I haven't either, and have done so w/o problems - after Toyota fluid changes, everything has been what it was. That link was just a suggestion that a software update may be laying around, I have no idea. I leave that to the OP to research, as people often post and never come back with a follow-up, making it a waste of time to answer questions in a very specific manner. if they follow-up, I get more detailed.