When Dodge put the 48RE in the 2003 trucks they didn't build them as strong as they could, only strong enough to hold stock Cummins power. And they put a cooler on that was good enough to keep them from burning up during heavy use with the converter unlocked.
The truck cannot come to a stop with a locked TC without killing the engine if it's in gear.
The TC is barely strong enough and is a good item to upgrade if the tranny is out of the truck. Other items are the input shaft and the intermediate band. A valve body upgrade will make firmer shifts which means less slipping and wear. Many heavy duty parts are available that can make this tranny hold enormous power.
There was also some weak flex plates installed but I can't remember the year. It might have been 2004. They can crack, so a close look is good, or replacement.
I've got 270,000 on mine now and have to be a bit careful. At 100,000 I upgraded the TC, but cheaped out and did not get a triple disk. Big mistake! My Cummins is turned up and I can slip the converter anytime I get on it too much at low RPM.
When it comes time I'll probably get Georand or other quality heavy duty trans, but not one from Chrysler, as it will be the same thing I started out with.
It would be so nice to slip an Aisin 6 speed auto in, but the earlier computers can't operate them.