Slam issue is well known and covered in here...

Summary: downshift is abrupt -- feels like you are getting rear ended (complete with whiplash on the worse cases).

try a fluid change -- yeah, I know it's lifetime fluid. Use the ZF LifeGuard 6 fluid. Do the filter too. You need to refill the pan w/the new fluid, then put the plug in hand tight, run the transmission through the gears with the engine on (still on jackstands -- just put your foot on the brake and shift through the gears, pausing for a second at each shift point) and return to park. Leave engine running and remove tranny plug. Add fluid until it runs out. BTW: cat converters are hot. Really hot. Be careful as you put the new fluid in. Transmission needs to be at 85 deg F +/-, so have a temp gauge handy.

This may help a bit or not. I ended up having the transmission replaced under certified pre owned warranty. Ugly proposition due to costs for remanufactured transmission, etc.

It's a nasty problem. Good luck!

__________________
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