To start, I bought an '05 MCS with 44k miles last summer - got a great price on it. At around 50k miles I noticed it was very hard downshifting (especially from 3rd to 2nd & 2nd to 1st). Seems to be a common problem. Using the advise in other threads on here I changed the ATF three times (2qts at a time) - down shifts like butter now.
note, I used Mobil ATF 3309 - had to drive all the way to Indiana to find it!

So here is my problem: The 1st ATF change helped a lot for the hard downshifting - 2nd ATF change helped even more. However, after the second change it began missing gears when upshifting (it would slip into neutral and RPMs would rev up - when I let off the gas it 'catches' and slams into gear). It only happens during aggressive driving at higher speeds (40 - 70mph). So I changed the AFT a 3rd time thinking it would help. I now have the same problem (missing gears), only at lower speeds (10 - 30mph) - I've not driven on the highway yet to see if it still does it at high speeds.

I'm going to reset the ECU tomorrow (adaption reset?), but thought I should ask first if anyone knows if it will solve my problem? Everyone says that resetting the ECU can't hurt but I'd hate to introduce another 'unknown variable' into the situation.

Pls help if you can!