My wife has a 99 Jimmy and she is having a problem with the 4 wheel drive. It's the 4 button NP8 I have done the disconnet of the battery, checked the fuses, I have replaced the switch on the dash. I took it to a mechanic and he ran the codes and told me that the TCCM was fried. I have the part# 15154323. I can't find this thing anywhere. Was there an upgrade to this part with a new part number? Hope someone can help me here. Thanks