Intermittent hard shifting then code U0102

[Jerm]

2008 Silverado 1500 5.3L 4x4 4sp auto.
A few weeks ago I went to start my truck and I got nothing, no cranking or anything. I grabbed the shift lever and went up and down with it a bit, then I was able to get it started. Once started it said "service 4x4" and "stabilitrak off" when driving it the transmission would shift very hard, like dropping into gear, not normal.
Took it directly to the dealership, they couldn't find the issue, but found I needed the throttle position sensor changed, because it was a recall and my truck hadn't had it done yet. Truck worked fine after that. Yesterday it did it again, same thing when I went to start it the "service 4x4" was on only for a few seconds, then when I drove it the transmission was shifting really harsh. I searched around the past few days and I think I determined its 1 of 2 things.
1.) The neutral safety switch is faulty and not telling the computer what gear its in, then goes to default mode.
2.) Transfer case control module (TCCM) is faulty. I have a generic OBD2 code reader and it stated U0102, lost communication with transfer case control module. But how does this have anything to do with this issue when I was in 2wheel drive the entire time?
I talked to the dealership today and they want me to "bring it in, we'll have a look at it" but I know what the answer will be, they won't see the issue unless it crops up while they are test driving it.
Is the neutral safety switch easy to change? I might have a look at it and do it myself if its not too costly.

My theory is that the neutral safety switch isn't telling the rest of the system what gear its in, so then the TCCM throws a code. Am I on the right track?