2018 transmission issues?

Apologies from the long winded post:
I recently (yesterday) drained and replaced my transmission fluid. This morning I drove about 400 miles including off road. Right at the end I had come off of a mountain pass onto level ground and my (auto) transmission is downshifting when it shouldn’t be. I put it in S to try and lock it in and it was still acting weird. When I tried to use cruise control it was just bypassing and continuing to speed up regardless. I will be driving at 40 with my foot off the gas and break and It continues to speed up whereas prior I had significantly more engine breaking. It would sit easy at 2k and then spike to 4k and not return until I hit the breaks until I was almost at a dead stop. I dont know if I just royally fucked something up bit I cannot find a similar thread

 

What kind of miles do u have on your truck?

 

I just hit 18k

 

why would you change the fluid already ??????

 

I was teaching a friend how to change oil and i wasn’t under the truck with him and he didn’t ask questions and drained the transmission fluid instead. My fault for negligence but regardless here we are

 

bad teacher, still under warrenty, take to dealer... lesson learned

 

I understand that, I just wanted to know if anyone had had a similar issue or any helpful insight on why. Thanks though.

 

Make sure you tell them what happened so they can examine the fluid.
They may “READ AS MAY” want to refresh the fluid and reset the memory so you start from scratch.

I see this quite often
Good Luck

On edit:

Don’t drive it unless right to the shop and the shop is close.

 

The transmission isn't like the easy to maintain version of old.

Did you follow these steps when you refilled?

https://www.tacomaworld.com/threads/3rd-gen-automatic-transmission-fluid-level-check-diy.547455/