The P1870 would cause the issue in the transmission but the lean codes would not.
I attached the info below of the P1870 code for your review. Please let us know if you have questions on working through this. Also, the 4WD issue is most likely the encoder motor but would not be related to the shifting issue so let's focus on that one here and then get new posts started for the other issues as we need to keep each issue to one topic.
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Thursday, April 22nd, 2021 AT 7:19 PM