I had the same problem with my 6hp26 ... fixed by dropping the pan, changing the filter ( and mechtronic sleeve while you are there ) and then fill it back up ( I used RL D4 ATF )

Then I did another fluid dump and refill in 20k miles and it has never shifted irregular again.

Temperature has nothing to do with it... the filter is obviously clogged after 100k miles

__________________
2006 X5 48is Black / Black - LED AEs - FCAB - GAS 1.2bar cap