i see you are really active on this group, so let me introduce myself: im a independent parts shop/service owner in europe. i have the EPC and WIS program from mercedes in my comp. have been workin with mercedes trucks, busses and unimogs for a long time. i really dont have a lot of experience with cars... (sorry if my english sucks, couse its not my native language)
but... IMO, if in was in the transmission was ATF, thats ok. when you removed old atf, and put new one in, you removed the "iron dust", so mabe that temporary had softened the symptoms, but the problem wasnt in the oil, but in the transmission box. i guess you usa folks have automatic... long story short: transmissin has to go down, open, and see whts going on.....