Drive train

Just to clarify the issue, the transmission shifts ok but you heard this bang and now the 4WD does not work?

If so this is an issue in the transfer case. However when this bang happened were you in 4WD?

https://www.2carpros.com/articles/automatic-transmission-problems

Next we need to check the codes and find out what are there, if any.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Lastly we may need to drop the pan and check for metal in the transmission fluid but we need to clarify this issue first because if the 4WD just doesn't work then that is not in the transmission.

Thanks

Hi thanks for the reply! I was in 2wd when I heard the bang! However I noticed the 4wd didn't work before that. I hear the 4wd low engage and indicator lights work appropriately! But front wheels do not spin with my rear ones in the mud!? Concerning the bang and slipping I have a po1870 code. Along with po 171 and 174 now! I don't think they are related to the transmission slipping!? I'm looking at a master solenoid replacement kit right now for the slipping!? All gears work just sluggish slipping into first!? Thank you!

Oh BTW! The fluid is clean and free of metal and debris. However, when I got this truck it was low on fluid and was sitting for 3 years in freezing weather. After filling it i put less than 500 miles on it and after this last winter noticed it was very low again!? Took about 1/2 to 3/4 to top off!? Thanks!

No leaks that I can find either!?

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.