1999 e36 3.2L automatic transmission problems

Some times when sitting still the RPM’s will dance between 600-400 until it stalls. It will also randomly drop a gear or 2 for no reason. The two problems will go on at the same time. It seems like the only way to get it to stop is to get the car up to 6,000 RPM. This seems to only happen in the fall and winter time. I have had my m3 for over 4 years now and this has happened about 20 times. But it will go away for many months at a time with no problems. I’m thinking fluid or tranny mounts (I hope it’s that simple). PLEASE HELP!