If there is a prob with the shift mode selector switch the ECM will but the transmission in a "limp mode" You'll have banging shifts, aparently this is to keep the transmission clutches from being damaged or make sure the transmission doesnt get thrown in reverse when its going 20mph? Youll usually get a hint if the selector switch is going out as your putting the transmission in gear and the P-R-N-D-3-2-L lights on the dash may dance around for just a split second. Typically it will make you raise an eyebrow and if youre like me shrug a shoulder and drive off. long story short i had a shift selector switch go out due to the "shift selector switch shaft seal" (say the 10 times!) gave out. no damage to the transmission but shortly after i got the banging shifts i noticed smoke behind me certainly not a good thing. a quick crawl under the car and noticed the exhaust pipe that goes right next to the selector shift was smoking with tranny oil... The mechanic said that the shift selector usually fails because it gets too hot from being so close to the exhaust or gets too wet from years of splashing water...
just figured id throw out a "this happened to me" story for anyone that could use the info. hope the lines get cleaned out. When you flush & fill use mobile1 synthetic ATF. Its worth the extra $40 just for piece of mind knowing your running the best stuff you can through the tranny...