I need to get the auto shaft out and measure it compared to a G-56 shaft in on 07 truck and see the difference. The NV5600 is 1.25" longer than the G-56 and it might be such a thing that the auto shaft is the same length as the NV setup.
I want to say my measurement was 79+" (QCLB).
52123162AA is the correct one for your truck. The Mopar shaft is only 4-4.5 inch in the bigger part, necked down to 3" at each end.
The Driveline services DS is a 5" full length and filled with foam to kill vibes. You can get it with the standard flange drive or have them just make an open yoke end and switch to the GM style u-bolt design. The flange drive has its issues.
The OE is 5" with 3-3.5" ends for 6-8" on it. It is not a full length 5" and according to DL Specialist it isn't adequate for the TQ these trucks make either.
Vibe issues are endemic with these trucks. The amount of NVH done to limit what eventually gets thru to the operator is eventually ends up being part of the problem, it just doesn't stand the test of time well. The other problem is the cheap AAM u-joints in the factory shafts, the lack of decent and adequate grease in them, and the effort to change them to something better without causing issues.
Add to that the standard approved technique to address vibration issues is flip the flange 180 degrees to see if that changes anything then replace the whole shaft if that doesn't work is telling. With 2 different trucks, different configurations, etc., we ended with the SAME problem being fixed by a 5" DS and loosing the flange that the problem is not more common. That defies the odds and experiences.
Removing the flange removes a known issue, for the extra $150 it is well worth the result in my experience.