Spent a few weeks poking at the 4x4 system. And fixed it today. My problem was the TCCM. All u guys talking about it only shifts while in neutral. Mine now goes in while in park or neutral. Had the same 4-high problem. Did the encoder, didn’t fix it, did the ball valve on the transfer case, didn’t fix it. The TCCM plug looked okay. But with the new one, the 4high worked without even hesitation in park or neutral. Hope this save some of you some time. Part was $40 at the junkyard. New was like $180+$200 core. Good luck!