Research methods of partial drain / partial fills- this seems to be the method least likely to cause the transmission to go into "shock", for lack of a better technical description. The filling temp is a narrow range- it's stamped on the bottom of the unit. ALWAYS check to ensure the fill port can be opened PRIOR to loosening drain port. I believe the plug is a 14mm hex. Hookup to DIS to check operating temp is within range, or best guess as "warm" by touch. Fill with a new garden sprayer. Be sure to have vehicle level. After a few partial drain / fills- I'd drop the pan and change the filter with FILTRAN oem ONLY- use new gasket.
Do more research, read more before jumping in-- this is not fun. Transmission fluid STINKS, its MESSY, and this task might or might not cure your problem- and can even make it worse-- but at this point, you have little to lose, right?
It's not what you buy, it's what you build- Unknown
EN90283 - Stabled for HG repair
DH06247 - Running like a champ