potential ECM issue

All the fuses are good? Grounds OK everywhere? I would be more inclined to think those sorts of problems would be signs of a bad BCM (body control module) rather than ECM.

I'll try to remember to take a look in my 2005 FSM this evening to see if I can find those symptoms somewhere. Are you getting any codes (CEL on?)?

I took a look in the FSM, but everything basically tells you to hook up a diagnostic tool (presumably the dealer's TechII) to see how the various modules are communicating.

My suggestion that it could be a bad BCM isn't much more than a guess. The ECM definitely doesn't input to the high beam indicator, for instance, and although the ECM provides input to the various gauges, it doesn't really control them, so I wouldn't expect a bad ECM to cause the instrument cluster to just completely shut down.

Is your Check Engine Light on (I would think it must be based on your description of the car's behavior), and if so, have you gotten the codes scanned anywhere?