99 Burb Transfer case slipping out of gear

[CNC-C10]

So I snagged up this 99 Suburban 4x4 last week. 205,000 miles but looks show room. Always garaged, original Gold Firemist paint with no oxidation.
5.7 with the automatic, it has the dual rocker switches for the transfer case.

For its maiden voyage I took it for a 80 mile trip to pickup and deliver parts for anodizing. On the way, it kicked into neutral twice.
65mph with the cruise on, coasting down a long grade. Then when the road starts to incline, it starts to give it gas..and that's when it goes into neutral.
Played with the gas and it went back into gear. I thought it was the transmission. So pull over and re-check the trans fluid looks new and full.

Fast forward about 20 miles and again 65mph in cruise coming up on 55 mph zone. Turn off cruise and let it coast for quite a ways, when it slows to 55 I punch on the cruise and again neutral.

So I let it coast to a wide spot and get out. Then you can hear the transfer case rattling. Shut it off and toggle the switches ( I have never owned on with this kind of setup) Crank it up and everything is fine.

Continue into town make several stops and make the trip home. On the way back I tried to make it fail again but no problems.

This truck was owned by a pilot and airplane salesman. I didn't get the receipts as he has died, but I got his hand written note pad with the mileage next to every little thing that he did
At 166 he had a GM 24228404 transfer case installed at the dealer.
I have done a bunch of online searching and most people start at the rocker switches with no results. Seems like it comes down to the control module.
Would that be consensus around here?
Thanks,
Gary

By the way..this frigging thing rocks Original exhaust that you know must be clogged up (underside has 0.00 rust looks showroom) I filled up before and after the trip same pump, handle clicks off and one more click off after that. 23.64 mpg