And then I started to install the aluminum diff cover

But wait, the bolt holes did not line up.

And the gasket looked different

And the whole thing was smaller than the steel cover I just removed.

Ya, the thing did not fit. I got $300+ for the new cover and $105 for the fluid; all I got was a fresh fluid change for the axle. Now that may not be all that bad, since axles break in, and changing the fluid afterward is a good idea. So I'll take that much, but No one, including the people who sold it, said anything about this 12" AAM has a bigger cover.

Why did they do that? A Dana 60 cover fits a Dana 70. The earlier 11.5AAM is almost as big, so why not keep common parts?

Don and I had a chat about these the other day and he encouraged me to add some details to the confusion ;-)
from 2019+ here are the new options:

11.5" AAM 2500/3500   12 Bolt R/G
(DRQ/ DRX Axle Code) 32 spline pinion
14 bolt Cover;  30 Spline Axles

12" Ram 3500  16 Bolt R/G
DRC / DR7 AXLE CODE 32 spline pinion
30 Spline Axle / Carrier Case
14 bolt Cover
(Don's truck)

12" Dropout  Ram 4500/5500   16 Bolt R/G
"DRY" AXLE CODE  32 spline pinion
33 Spline Axle / Carrier Case

the AAM rear has a carrier break for the 1st time since it's inception in 2003; 4.10/down 4.44/up, and most have a new "trac-rite" clutch type limited slip like Don's here. We do have new gears for them, up to 4.44 ratio front and rear, and factory limited slips, but the supply is low from AAM, i'd say we do 2-3 regears a month, whereas on jeeps for example it's 20-30 a day for comparison.

since our setup specs have not been updated for a while, here are the details on these new differentials as well:

Set up specs : w/ OE gears

11.5:
Back lash – 0.007-11
Pinion Bearing Preload  - 15-25 in/lb
Carrier Caps  - 207 Ft/lb
Ring Gear Bolts  - 59Ft/lb + 64 degrees – OEM bolts are Torque To Yield – DO NOT RE USE  - OEM bolt # 5086783AB


12”:
Back lash – 0.008-12
Pinion Bearing Preload  - 23-37 in/lb
Carrier Caps  - 180 Ft/lb
Ring Gear Bolts  - 74Ft/lb + 57 degrees – OEM bolts are Torque To Yield – DO NOT RE USE  - OEM bolt # 68455381AB

‭Amos 5:24 ESV‬
[24] But let justice roll down like waters, and righteousness like an ever-flowing stream.

NW MT

D $3.95
G $3.50

Both have been floating within 5 cents a gallon of those prices for a couple weeks

I then added 20 psi to the bags to test for leaks overnight.

That raised the rear end a bit more.

Obviously, the back end will settle down with 4,000 lbs. in the bed, but I can say, I am pleased with the results.

Here in Oklahoma $3.49 for premium 100% gas. I just paid $3.22 for diesel

Yep, good ol Kali, ouch.