Several months ago I was experiencing hard shifts and rumbling at low speeds. My car currently has about 88K miles. I did a lot of research on the internet and came up with several possible causes. I decided to remove the valve body, completely disassemble, clean, and replace the following:
1. New conductor plate and adapter plug
2. Replaced all solenoids with re-manufactured parts
3. Installed aftermarket valve sleeve kits
4. and of course new filter, pan seal, and fluid
Torqued all bolts to factory spec and reassembled. refilled the fluid step by step and everything was perfect until I shut the ignition off and the trans puked up a puddle of trans fluid and coolant.

So no big deal, I bought a new radiator and had it in and running in less than 45 minutes. The car has run like new for the last few months and all of a sudden the hard shifts and rumbling is back. I'll add at this point I share this car with my wife and we have very different driving styles. So today I drove it to get up to temperature checked the fluid level and it was dead on. I have a DAS (not an advanced user but can do basics) connected it and ran a diagnostic, to my surprise there were no faults. I decided at this point to reset the adaptions. I disconnected and drove the car and once again runs good as new.

My question is: is it possible the TCU is going bad, maybe do to the two very different driving styles and the age of the vehicle? or is there something else I am missing that would cause this.

Thank you in advance any help.

Comments

What can happened and may have happened in your case is that coolant and transmission oil have mixed together. If coolant gets into the trans it will destroyed it within a few thousands miles. Yes you will not get any codes, until the car stops moving. 

If it was my car I would take a sample of transmission fluid and test it for glycol which is found in coolant. There are plenty of labs that you can send samples to. One that I have used is Blackstone. 

You should also check the 13pin connector at the side of transmission for oil contamination. Easy fix.

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