V8 00USH, I have to ask, why did you add in the Mocal brand thermostat? Why not just have the factory return line connect directly to one side of the external tranny rad and then the other side of the external tranny rad connection just connect up with the factory return line again. A simpler design no? AND then you are always cooling the tranny fluid with factory cooler and then external cooler... OR am I missing something here?
Glad it fixed your issues. I know FMugur was having similar issues but doesn't seem to have the same fix to his harsh tranny slam problem (according to another thread) sadly.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S