2011 Dodge Ram Hemi 5.7 L Longhorn Edition. What's killing my battery?

Parasitic drain. You have a circuit pulling more than 50 miliamps which kills the battery. YouTube it and do the tests. It is easy. The fix might not be as easy but finding it is simple

Do you have something plugged into accessory ports when truck is off? Some cars allow voltage to be supplied when vehicle is off. This issue could be something as simple as a switch in the on position but the item is not physically on while vehicle is off.

Find out what the trouble code for the check engine light is. Any local autoparts store will scan it for free and let you know what the trouble code is. Get the code and do some "googling" for more information. Also post the code here and we may be able to help you. How many miles on your Ram? Pep Boys would not be very high on my list for where to take my vehicle for repairs.

Bob that was good about what you said about Pep Boys. I got a good laugh.

Many years ago there was a PepBoys near me and their service work was way below what it should have been. Although expensive, dealerships are usually the best place to go for repairs. They know the vehicles they sell better than anybody. They also have the special tools, service manuals, and hotline to the engineers to get things fixed. They are not perfect however.

Had same problem, found out fuel pump was pulling power from the fuse box the relay corroded and drew constant power with the truck off, it can be bypassed