These symptoms are typical of a connection problem on the IPM (Integrated Power Module - AKA Fuse Box). It is good maintenance to (with battery disconnected) disconnect and re-connect all the wiring connectors on the bottom of the IPM. This is where ALL of the power comes from for everything and after a few years the connections can get a bit corroded and cause very strange intermittent issues. Teh act of disconnect/re-connect cycles the contacts which can solve many issues.
I'm not saying that this 'IS' your problem, but it costs nothing to do this bit of maintenance and could save you many $ and headaches.
I should also note that the Instrument Cluster is a relatively high point of failure on the 3rd gen Rams. However I firmly believe that many Instrument Clusters and IPM's have been replaced because of poor connections, and the act of replacing them cycled the contacts so the replacement appeared to be successful.