In automatic transmission vehicles, does switching to "3" help when going up steep inclines?

with a very generic question, a generic answer...

in most vehicles, 3 will shift out of overdrive into a lower ratio gear.

thus allowing the vehicle to climb easier...

in some cars this will unlock the torque converter as well.

Placing the shift of an automatic in L (low), 2 or 3 (assuming it's a four speed automatic) will hold the transmission in that gear. I can see placing it in 3 or even 2 for climbing a long steep hill since in Drive it might be continually shifting up and down which would be annoying. Another advantage of being able to hold it in a given gear is lets say you want to start off in a slippery snow, sand or mud situation. Staring in second might let you ease off with out the torque of first gear spinning the tires and digging you in.

Basically, if you put the transmission into a lower gear, you sacrifice top speed and fuel economy for torque which is the single most important thing to squeeze out of a transmission when trying to climb hills.

The key word in "automatic tranmission" is automatic. This means that in most cases, including steep inclines, you shouldn't mess with it. In any modern automatic transmission the car knows which gear it should be in.

If your car is less than 5 or 6 years old, there is no benefit to taking your car out of "drive". Your car is smarter about these things than you are.

The previous poster brings up a very good point. Automatics still do shift even when a lower gear is chosen and today's automatics are much smarter about downshifting than earlier transmissions. Great point.

It is also very hard to out perform an automatic in dense traffic, not to mention clutch wear on a manual.