In 2009 my 59,000 mile 2007 Ram had a strange problem. The engine ran fine, then suddenly started running really rough as if it were missing on 4 cylinders. It felt like I was trying to drive on 4 flat tires it shook so bad.
The MDS system had a failure where one of the lifters to an MDS cylinder failed. It hung open, allowing no compression in that cylinder and a contamination of adjacent cylinders. As cyl 4 came up on its compression stroke, the intake charge pushed back through the open valve and onto the intake. The link pin on the lifter had failed. Instead of it either working normally for regular combustion or shutting off to save fuel, it was in between. The dealer fixed it under warranty, new lifter and a few other things.
I am not sure if the 2003 had the MDS system yet.