If the check engine light came on, your engine's ECU computer is registering 1 or more error codes. If you have an OBD-II scanner you can read them yourself, otherwise you'll have to take the truck to the dealership to clear them even if you fix the mechanical failure on your own.
I'm assuming it's an automatic transmission, which may or may not be owner-serviceable (I know Fords require a trip to the dealership for transmission service). However, if you're experienced in working on your truck, you may just want to look underneath to see if the driveshaft, u-joints, rear end differential, and transmission box seem to be lined up and fastened properly. The pop you heard was most likely a mechanical failure in which a mount or internal gear may have broken or seized. If nothing seems broken, twisted, bent, or leaking underneath your truck, your best bet is to get the error codes causing your check engine light scanned asap.
Good luck, transmission failures are never fun and rarely cheap. I do believe they are covered in Dodge's extended powertrain warranty, so there may be some salvation.