I've heard too many horror stories about pressure flushes and reverse flushes from shops for transmissions. Also, just dropping the pan and doing the filter doesn't get to the tq convertor.
So, I read a while back about using the transmission pump to naturally pull and push new fluid in and out of the transmission. My questions is: Can this be performed via the inlet/outlet lines of the aux trans cooler? Basically, fill a bucket up with good trans fluid of your choice and have the other end in a "bad fluid" catcher or oil pan. Start the truck and let the transmission pump naturally pull the good fluid in and push the old fluid out. When it's done, you can then crack the pan and replace the filter knowing that all of the good fluid has pushed the old/bad fluid out and a good filter can then go in its place.
Does that make sense?