If you go from Non-Nav to 12C Nav you are going to have a lot of issues to contend with. For starters, you will have to deal with the installation of a GPS antenna to the top of the truck where the radio fin is. If you do not have Sirius included in your radio, it is going to be even more steps to gain Sirius. There is a difference in the wiring harnesses, and if you do not properly program the BCM, you will blank out your entire computer that controls the electronic functions of the truck. I am doing the upgrade tomorrow from the 4C Nav to the 12C Nav. Sourcing parts has been almost impossible and it has taken me more than 6 weeks of hard searching to find a module for it. The current module in the AJ suffix has been discontinued, which means the only way to get one is to be lucky enough to find a totaled truck and hope you get to it before everyone else does. Yards and people know how valuable these modules are, and you should expect to pay pretty much retail or even more depending on who is selling and how badly you want it.
Another issue that you are going to encounter is with your dealer. You could void your electronics warranty if they want to give you a hard time. I spoke to both of my dealers who know what I am doing with mine, so they are expecting to see it come in next with the 12C. If I have issues with the radio, I am completely on my own since the warranty will not cover it at all. Once they plug the VIN in and see that you have reconfigured, they can be difficult and tell you to go pound sand. It all depends on your relationship with your service writer and the dealership. Some techs will ignore the VIN fault code when they scan it, and others will be "by the book" and flag your VIN which leaves you immediately out of warranty for modifying the vehicles electronic system,
If you have questions feel free to ask