Need help diagnosing this car..gauges and lights are intermittently erratic and transmission shifts hard, also abs/trac, low fuel, check engine light all flash, power steering deactivates and engine goes into limp mode, sets multiple communication codes in all modules when problem happens. BCM stores many codes for electronics such as trunk release, courtesy lamps, cruise switch fault, etc. seems to be either a power supply issue or CAN line issue. Can duplicate issue only in gear when accelerating, won't act up in park or neutral, but will happen when power braking as long as it's in gear. I replaced the ignition switch, disconnected the bcm and pcm and put dielectric compound on the connectors, also checked all grounds I could see and performed a battery reset. Also, when it happens in gear parked and power braking, all gauges go to zero, instrument lights flash, and loss of communication occurs, when shifted into neutral, everything returns back to normal until accelerated in gear again.
Has anyone run into this?? Thinking there is a poor connection or loose ground somewhere and transmission movement moves loose connection.
Car is a 2009 Saturn Aura with 44k miles

 

That sounds like one of the worst BCM failures I've ever heard of.

Dashboard = Christmas tree is a big hint since all that good stuff is controlled by the BCM
Coming in and out like that usually means it's about to give up the ghost.
If you just purchased it from someone, they knew about this and waited for it to settle down and cleared the codes before showing you the car. It's why they were selling it.
I think you can scan the ecm for miles since codes last cleared.

Auras are notorious for electrical system nightmares.

It could in act be a grounding issue, but sounds like BCM.

I think either the Chevy Malibu or Impala was derived from this design (check wikipedia) so if you have a benjamin to waste, take it to a chevy dealer for a diag.
Just by the sheer number of codes, esp if many are body (B) codes points towards BCM.

44k. what a shame.

The BCM CAN be replaced, but it's not terribly cheap. Best bet would be to pull one from a junyard car, swap it in, do a BCM relearn and PASSlock relearn in that oirder and see if your problems vanish