Hi!
Well, if transmission slips even little, I agree you opinion about friction plates... but no slipping at all... just very hard upshift and great bang when downshift to first gear.
After all, I`m somekind of professional about automatic transmissions, but these with "brains" make me little hesitating.
If I`m right, you have fluent germany? Do you have seen any similar problems in german forum? My germany is even worse than my english

Jamo