I'm assuming when you post 'no codes', you're using a real code reader like a GT or INPA, not the little cheap thing I have at home… If not, get a real code reader to read codes so you have a chance at diagnosing it.

Since you have both transmissions, all you have to lose is labor pulling them both out and comparing…

I guess you could attempt a rebuild, but there are specialty shops that can do that for less hassle is my guess.

If it were me, I'd do the following:

1) check that transmission fluid level is correct, if no add and see what happens. If yes, go to step 2.

2) start calling transmission rebuild shops and ask them what they think. If it sounds reasonably affordable, then drop tranny off at their place. If it is too much, then go to step 3.

3) drop and swap. Do a fluid, filter, etc. change.

Good luck and let us know how it goes!

__________________
Kirk
Las Vegas
2016 X5 40e Mineral White/Black Dakota Leather, ZLL, ZCW, ZDA, ZDB, ZPP, multi contour seats, rear side window shades, HK stereo
2011 E90M3, 6-speed manual