2003 Suburban v8 4wd

180k

Years ago the transmission was replaced and shifts flawlessly while in 2wd. But after replacement the car would slip out of gear and be unable to move after engaging 4wd. It would need to be shifted to drive then 2wd to move again. Then the car started shifting itself into 4wd randomly which doesn’t work. I’m figuring the transfer case module is causing the random shifting into 4wd but is there something to check that might’ve been installed wrong or messed up after the transmission replacement that’s caused the 4wd to not work at all? I’ve heard of this being a common issue and most people just delete the 4wd entirely to bypass this. I’m trying to not have that done but if it’s the easiest then that’s fine.