Pontiac Repair: Computer error, security light, control modules

Question
QUESTION: While driving my wife's G6 the security light came on and the gauges cycled.  After a few miles, the gauges went 'dead, power steering read in the display and the odometer read error.  After that the car started cutting out and the brakes were hard to press.
When shut-off and restarted the car drove fine for about another 20 miles and repeated.

ANSWER: could be several things, have you replaced the battery recently?

---------- FOLLOW-UP ----------

QUESTION: I changed the battery about 3 months ago.  Also changed the cam position sensor (bank 1 intake), because of a problem with the shifting.  Fixed that, now it is doing this.

Answer
Hi Jason:

What year is this G6 and what engine is in it?
My guess is you have a communication data line issue with this car either a bad connection or one of the control modules is going down and it's cutting out the communication betweeen all the modules on the network. When the IPC (cluster) looses communication it will display error on the odometer.. do you know what codes are set and it what modules they are set it? that can narrow it down possably. with out knowing what codes are stores it's impossable to tell you even what direction to head towards..