2000 Dodge Ram 1500 Transfer Case

231D or 231HD? I had my transfer case go to pot and I'm trying to figure out what to do. The manual and the dealership say it needs a 231HD. All the shops I've talked to and all the websites (that aren't Dodge-sponsored) say 231D. Are they the same or what? It's for a 2000 Dodge 1500 with the 5.2L engine.