I found the window sticker in the glovebox of my 2011 2500 Megacab Cummins Ram. In the left column ( std. options) it has 10.5" differential but the right side (optional equipment) it has 11.5" differential with limited slip. It has a 14 bolt cover, which rear is in my Ram?

you can get your build sheet from dodge:

https://www.dodge.com/webselfservice/dodge/index.html

Click on the link down the left side of the page that says "Equipment List"

Enter your VIN in the smaller search bar and click search

But that should be an AAM 11.5

Codes:
[DME]=Axle Ratio - 3.73
[DMF]=Axle Ratio - 4.10[
[DRW]=Axle - Rear,10.50
[DRQ]=Axle - Rear,11.50
[DRX]=Axle - Rear,11.50, Dual Wheels
[DSA]=Axle - Anti-Spin Differential

10.5" was standard on the 2500. Selecting the Cummins option automatically added the 11.5 AAM.

Thanks guys.

Dodge was doing some funky things like Dana 70 with a Dana 80 center section.
In your case my online lending library confirms that your center section at least is the AAM 11.5" used also on GM trucks.

https://www.drivetrainshop.com/GM_Chrysler_AAM_11_5_s/104.htm

R.