Hello, my name is Ryan and I own a 2002 impala, 3.8L. Approx 140,000 miles on it

I commute to work and drive about 50 miles one way.
When I get to work and shift from drive to reverse (I always back in to my parking spot) the RPM's drop, sounds like its going to die for a second or so. I give it some gas and its fine. From what I've read its hard to diagnosis as it could be a dozen different things. Mostly I've heard the MAF and Idle Control Sensor could be the cheaper/easier things to replace...

Any help would be greatly appreciated, thanks!