Well, there is a U1026, but there is no V codes. Here is what the U1026 about:
CIRCUIT DESCRIPTION Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module's Node Alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a Node Alive message every 2 seconds . When no message is detected from a learned identification number for 5 seconds , a DTC U1xxx where xxx is equal to the 3-digit identification number is set. The DTC U1026 indicates a problem in the Transfer Case Shift Control Module (TCSCM)
You really need an OE diagnostic computer to troubleshoot this problem. I"d find a good GM specialty shop in your area and let them do it.