I don't think the air bag has anything to do with it.
When going uphill, is that also in automatic mode?
Otherwise, it sounds like "normal" automatic behavior; it will only downshift if you brake suddenly or accelerate suddenly to affect a large change in torque. If you're in traffic and want to keep good mpg, it is best to keep it in a manual mode and shift it as you like. Automatics are notoriously fidgety (unless CVT) for unpredictable, traffic-laden driving; even though it is easy for the driver the transmission gets confused.
1998 BMW e36 M3 Sedan
Crap, I think I may be a yuppie...
2003 MINI Cooper