As far as transfer case, my information does not support much on who owns who. If they break we fix em.....here is what i got from SI.
Document ID# 1579179
2007 GMC Truck Sierra - 4WD
Transfer Case Description and Operation
The New Venture Gear (NVG) 261, RPO NP2 transfer case is a 2-speed, part-time with mode shift-on-the-fly capability. It has a chain driven front output shaft and an epicyclical low range planetary arrangement. The NVG 261 transfer case features a 4 position shift lever control located in the vehicle floor plan. As required, the operator can select 4HI position from 2HI on-the-fly, as described in the owners manual. A dash mounted 4WD lamp continues flashing during shifting, until all criteria have been met and the new mode/range position has been reached. Once the new mode/range position is fully engaged and the front axle disconnect locks in, the dash light 4WD indicator lamp remains ON constantly. Range shifting functions similarly, although it should be limited to speeds 5 km/h (3 mph) or less.
The 4 manual mode, or range gear positions, of the NVG 261 transfer case are:
• 2HI - 2-wheel drive high range
• 4HI - 4-wheel drive high range, part-time
• 4LO - 4-wheel drive low range, 2.72:1 gear ratio reduction
• N - NEUTRAL, 4-wheel
When the ignition switch is in the run position and the 4WD shift lever is in 4WD, the transfer case switch closes, supplying a ground to the axle actuator control circuit. With the ground applied, the logic of the front axle actuator actuates a DC motor to engage the front axle and supply voltage to the axle switch signal circuit. The axle switch signal circuit notifies the powertrain control module (PCM) and the anti-lock brake system that the vehicle is in the 4WD mode. The 4WD indicator is commanded on via a Class 2 serial data signal from the PCM. When the 4WD shift lever is in 4WD low, the transfer case switch closes and supplies a ground on the 4WD low signal circuit; this informs the PCM that the vehicle transfer case is in low range. When the vehicle is in low range, the PCM changes the shift pattern of the automatic transmission.
During normal driving situations, the transfer case can operate in the 2WD mode. The driver may choose to select any of the mode/range gear positions while driving the vehicle. However, the transfer case should not be shifted into or out of 4LO unless the following criteria have been met:
• The automatic transmission is in NEUTRAL or the clutch pedal is depressed.
• The vehicle speed is less than 5 km/h (3 mph).
This transfer case also has a NEUTRAL position. A shift to NEUTRAL allows the vehicle to be towed without rotating the transmission output shaft. In NEUTRAL, the rear propeller shaft rotates the transfer case rear output shaft, which rotates the oil pump, providing constant lubrication during towing. Note, this NEUTRAL position is a 4WD NEUTRAL, meaning the front and rear outputs of the transfer case are engaged as though in 4HI. With a disconnecting front axle, there is no power flow to the front wheels, allowing towing with the front wheels off the ground or flat towing without driveline binding. Again, the transfer case should not be shifted into or out of NEUTRAL unless the following criteria have been met:
• The automatic transmission is in NEUTRAL or the clutch pedal is depressed.
• The vehicle speed is less than 5 km/h (3 mph).
The NVG 261 transfer case is available in 5 variations, depending on the engine and transmission configurations. The variations allow the transfer case to handle different torque loads. When servicing the transfer case it is important to understand which variation is being serviced because of the difference in components.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1579179&evc=sm&pubid=1647&cellId=62365&mspsdsubkey=6439#tab1-1579179">NVG 261 Variations
Model
Transmission
Input Gear
Output Shaft
Chain Size
Hi/Low Planetary
Application
Light Duty (LD)
M30 - 4L60E
27T
Spline
32T
Spline
3/8 X 1.25 in
3 Pinion
K1
Light Duty (LD)
MG5 - NV 3500
32T
Spline
32T
Spline
3/8 X 1.25 in
3 Pinion
K1
Heavy Duty 1 (HD1)
MT1 - 4L80E
MW3 - NV 4500
32T
Spline
32T
Spline
3/8 X 1.5 in
6 Pinion
K2
Non Heavy Duty
Heavy Duty 2 (HD2)
MT1 - 4L80E
MW3 - NV 4500
32T
Spline
32T
Spline
7/16 X 1.5 in
6 Pinion
K2
Heavy Duty
Super Heavy Duty (SHD)
ML6 - ZF S6-650
M74 - Allison
29T
Spline
31T
Spline
7/16 X 1.5 in
6 Pinion
K3
The SHD model shares many of the same components, but the increased torque capacity of the SHD requires a double row input bearing and larger diameter rear output shaft, rear output shaft bearing higher capacity, larger rear seal and case halves machined differently.
<A href="http://service.gm.com/servlets/BlobShtml?ShtmlFile=1579179&evc=sm&pubid=1647&cellId=62365&mspsdsubkey=6439#ss2-1579179">2WD Mode Power Flow
There is a bunch more, didnt want to bore you too much;)