TL DR - Transmission feels sluggish to downshift, will hold at 2500 and 3500 RPM's before downshifting for heavy acceleration, shift solenoid replacement?

Been having an issue for about a few months now that my transmission is sluggish in response to accelerating, really got annoyed when I drove 3 hours out to Ocean City and passing people was a guessing game of when the tranny was gonna kickdown to try and pass people.
I've read up on other forums, watched DIY videos (Apparently the LS400's had a Solenoid #2 issue) and even Transmission Q/A's for what could be causing it, many signs point to the trans solenoids needed to be replaced and possibly a little fluid change to help.
However, many of my close car friends and popular rumors have warned of changing the transmission fluid since, I dont think the transmission fluid has been serviced in this cars life, nearing 160,000 miles, and, they say doing that will cause the trans to slip and other such shifting issues, however the color is still pinkish red.

Will just dropping the pan to access the solenoids, replacing what fluid was dropped out from the pan and putting it all back in cause any major shifting issues?

 

Try cleaning your MAF first. If the engine doesn't respond to throttle inputs, the transmission won't either.

 

what year is the car?

does is downshift if you put it into manual mode and shift down?

 

LS430 ECM may be one of the first major reasons of any LS430 problems related to transmission shifting. Sending it for repair to SIA and properly resetting adaptation memory (preferably after fluid change) likely fix downshifting and upshifting. SIA may recommend to flash the ECM to factory spec as well.

However, I highly suggest to use Techstream to read any transmission related codes before you start replacing parts in the valvebody. If no codes exist, the solenoid's function is not above the failure threshold, according to the system.

 

If you can see the transmission fluid is pinkish red then you likely have a dipstick or a major leak. Let’s assume you have a dipstick. Transmission fluid builds acidity over time and loses some of its detergent package. Just because the color is close to new doesn’t mean the fluid is operating properly. Simply drain and refill and maybe the old/new combination of fluid will clean the internal transmission passages enough to operate properly. If it improves with one drain and fill but is still not quite right, do another drain and fill and see if it improves. By slowly replacing the fluid you won’t be shocking the transmission the way a flush machine does and for a small investment you can determine if the issue lies deeper. Cleaning the MAF and changing the oil/filter and transmission fluid are mandatory maintenance items to put on your maintenance calendar. I go 7500 miles on synthetic oil and clean the MAF and do a drain/fill on the transmission every 10,000 miles. Clean the MAF now and do a drain and fill and report back.

 

So, update. Purchased a new DENSO MAF sensor from Rockauto.com. Put it in, little changed, car felt smoother on idle but idk?
And today leaving for lunch, the car was responsive at first but then became extremely sluggish and just was absolutely sloppy with shifting. However, when returning to work, it was smoother, it's 50/50 time to time that it'll be sloppy or actually responsive.

I'm planning on taking my car to a local transmission shop for diagnostic work to see what it might truly be. So fingers crossed on that! However before that, I'm going to have someone check the OBD port to see if Im getting any transmission codes, I've been dealing with a P0440 code for a loooong time so if anything else has popped up, the CEL light has been on for that emission code so I'd never know if anything new has appeared.

Bug again, fingers crossed on this.

 

Any update to report?