Had to replace the TransFer case module behind the head light switch in the dash. TCM code co355,you need a decent scanner to access this module through the OBDII connector. The module was installed at chevrolet because it needed to be flashed or burned with a program,guess what they are the only ones who can do it.
Regardless the vehicle was repaired see TSB #02-04-21-006E.
not warranty,had to pay for this one.
Source: TSB 02-04-006E