I'm afraid of shocking the trans with all new fluid. Some people say that it will do more harm than good when it is all changed at once, so they claim you should do it in small increments. Is this just a myth?
I think most of the stories you hear are about Very Poorly Maintained pieces that were probably on the brink anyway.... Drop the pan & see what the fluid looks like(the dip stick always looks pink)....if it looks clean then stop there & add the 4-qts back....If it looks black or brown you may as well drain the converter & start fresh...IMO
Then if it blows up in the next 5-yrs you can blame me