I can say from experience that having a shift kit of some kind in the trans makes a world of difference, when you just use the tuner to change the shift points and firmness your putting strain on the stock components that are not meant to run at that pressure. Most valve bodys will develope a squeal, once it goes to shift you can hear the vb forcing the fluid though, thats not a good thing. have to remember the stock holes in a vb are not as big as those on a shift kit, so your forcing more fluid though a smaller hole. I blew the trans in my 95 tbird by doing that, after that i got a new street/strip valve body and that did the trick, the combo of the tuner plus the stronger more effective vb is insane, plus is anyone has studied Jerry W's J-Mod threads on TCCOA (Jerry was a Ford Trans Tech that helped build the 4R70W) he states how much better having a kit in your car is.