07 aspen recently started developing several issues simultaneously. The SVC 4wd light has been coming on, and then it started trying to shift into 4lock, and now 4lo.

Additionally, you can hear the shift motor trying to shift the transfer case when you lock/unlock the doors with the key fob. I've read some people say the problem is the FCM, some people say the problem is the TCM, and some people say it's both. Is there any definitive way to test which one it is without firing the parts cannon at it?