All trim levels of RAM 1500 double and crew cab models are completely built in Michigan, except for my truck (the Crew Cab Laramie) which is built in both Michigan for the US buyers and ALSO in Mexico for the Mexican market buyers. So my particular Laramie truck was made in Michigan.
All 1500 regular cab trucks are made in Mexico.
All 2500, and 3500 RAM trucks, gas or diesel, are made in Mexico, but the Cummins diesel engine is made in the USA. So every newer 3/4 and 1 ton RAM truck you see on the road was made in Mexico.
The RAM 1500 eco-diesel engine is manufactured by an Italian company called "VM Motori" which is now owned in a 50%-50% joint venture by Chrysler/Fiat and General Motors.
Dodge RAM has been building trucks in Mexico since NAFTA took effect in 1995. Though I'm not sure when the manufacturing details above came to be. I'm sure it changed over time.
RAM truck division split from Dodge in 2010 but are still owned under the Chrysler/Fiat banner. After all the details were hashed out, the name "Dodge" was removed from all of the 1/2 ton and larger trucks. You wont find anything but the name "RAM" (a division of Fiat) on any of the trucks 2012 or newer and you won't see registrations on VIN numbers listed as Dodge Ram since 2014. Don't know why the VIN numbers took longer. I'd be willing to bet the whole split of the RAM truck division had something to do with tax dodging...no pun intended