Transmission disengage on 2004 Tahoe

Over the past month I’ve had 4 instances when my Tahoe is is 2-wheel drive where the car felt like it was in neutral. # times going down the road at about 45 miles per hour and once when I was trying tack out of a parking space. I took it to the dealer where I purchsesd the car new and they have alway done all the mainteance on it. They could not locate the problem. It seems to work fine as long as I have the vehicle in 4-way drive automatic but then I am not sure if it is just kicking into 4-way drie and I am not noticing it. Any ideas on what is wrong or shoud I just stay in 4-way drive automatic?