I m not sure if the tranny was acting up before i changed the pcm i bought the truck not running with a bad fuel pump and the guy i bought it from was trying to fix the truck and put a pcm in the truck witch was the wrong pcm he put a v6 4.3 pcm in a v8 5.7 and the truck wouldnt run right so i changed the fuel pump and the the pcm now it runs great the scanner i have is a red snap-on scanner that reads transmissions and engine codes and does lots of tests but no codes come up for the tranny i m not even sure my tranny is even in limp mode