Here we go:
So I originally set out to find out if I could replicate what I had seen some others do online on older generation trucks (GMT900 specifically) by swapping the two-speed NQH (MP3023) transfer case into a truck that originally came with the NP0 (MP3010) single-speed. I have a 2018 Yukon XL, 5.3L with the 6L80, sitting at roughly 150k miles. I've started doing mild off-roading so wanted the 2-speed. I could not find anyone online having done this exact swap (NP0-NQH) on the K2XX generation of trucks and SUVs.
I managed to do this without any reprogramming, but only because I did a few specific things. I required three components for the install in order to do it without programming:
- The 4WD selector switch with 4Lo (obtained from wrecked 2017 Silverado)
- The TCCM, already programmed for the NQH transfer case (from the same 2017 Silverado)
- The transfer case itself (which I obtained from a wrecked 2013 Silverado)
I did need to swap the encoder from my original transfer case because the one on my donor case had a crack in the connector and I didn't want water intrusion.
There are currently no error codes present on the vehicle, and no reprogramming was required for any modules. Drives great!
The biggest challenge I faced was shopping around for the donor case; many people would be selling on Facebook Marketplace or elsewhere but not be 100% sure which transmission the case came off of, or which option (NQH vs NP0) it was. The latter is extremely hard to determine externally, but you can tell using the three-letter broadcast code on the top by cross-referencing that to the fitment data section on ACDelco's website when looking at the transfer cases. For example, AY9 and AHD represent NP0 transfer cases for a 6L80, whereas AY6 represents an NQH t-case for 6L80 (there are a whole ton of different broadcast codes but those are just some I came across). A number of different ACDelco part numbers will be interchangable; I think they were switched up a few times over the years.
I will note the transfer case I installed was a piece of crap; I replaced the fluid and found a fair bit of very fine metal shavings on the magnet so I do think I might end up swapping it again later. The exterior of the case also got beat to hell in shipping and one of the studs was bent, which I was suprisingly able to bend back straight. Some other minor exterior damage was present, but I noticed no significant play or weird noise driving.
The actual install itself was straight forward, I did it without the vehicle lifted off the ground (has a 2 inch lift). Removing the 6 nuts holding the t-case to the transmission adapter is damn near impossible without a stubby flex-head 15mm ratchet wrench, so get one of those if you do something like this. Everything else was doable with tools most would likely already have. I lifted the new t-case into place with no jack; we needed three people to do so.
Big thanks to
swathdiver for info he contributed to this thread and other threads I've seen online about these transfer cases, you were a huge help!
