My Armstrong Ultra II furnace (about 20 years old) goes through it's start up cycle, inducer motor runs, ignitor sparks the pilot and main burner. So far so good. After a minute or so of the burn cycle, the ignitor starts sparking while burners are on, and after 10-30 seconds, the whole thing shuts down. I've had the flame sensor replaced, and things worked for about 1 day! Now, I'm back to the same problem again. Is it a bum sensor replacement, or more likely the gray control module (Robertshaw)?

I have seen this before, you are right it is more than likely it is the Robertshaw Control.