Need help please!

[TractionGod]

I need help!!!! Drove to Texas last weekend and it rained the entire way. 2 days later my truck started "banging" into gear when shifted from reverse to drive. At the same time I noticed my check engine light is on, my doors dont auto lock (sometimes they do but not all the time), they dont unlock when I shift into park and I dont have any back up lights. Changed the fuse for the b/u lights but still dont work. I also noticed at that time that the gear indicator only shows when I'm in park and drive. So I drove it home and it worked fine. Got in it to go to work yesterday and I guess (from what I read on here) its in limp mode because its in 2nd gear and wont shift even manually. My truck is an 04 duramax 2500HD.
PLEASE HELP! This truck is my family's only transportation.
Thanks.

[deeretracks]

The trans is prolly going to be the NSBU.

[RBinTX]

I had the exact same issue when the transmission module went out. The module used to be either internal and it is now external or viseversa. Dealer covered it since it was a known issue. I had the exact same symptoms.

[TractionGod]

OK I changed the nsbu switch today and it didnt change anything. Still the same stuff happening. I didnt clear the codes or anything. Would that make it stay in limp mode? Do I have to clear the codes or will it do that by itself? I never even checked the codes, I just went by what I read on here. HELP...I'm desperate!!