2003 Chevrolet Tahoe 4wd problem

What solutions have you heard for this issue? a 4wd system that switches into 4wd on its own. It also will not come out of 4wd and back to 2wd at times. We have to put the car into park, turn it off, then turn it back on sometimes to switch the gear box. It is a new transmission, and this problem has persisted for a few years prior to having the transmission replaced.
It seems to be an electrical problem, what should we replace?

Thanks