The RB4 navigation system is a factory option, and does not display maps. Most reports from members here are that it is pretty lame for the price.
The RB1 is a dealer installed accessory, and has full map capability, and reports are that it is a very nice unit. Problem is, you need to order a truck with a radio, and then pull it out to install the RB1. If you want an Infinity system, you need to order a $900 radio upgrade, just so you can throw away the radio and install the RB1.
Can anyone explain why Dodge doesn't offer the RB1 with infinity sound as a factory option? They must be smarter than me, but I sure can't see it.