[spacemanspif]

One good thing is that your commute is basically a set-and-forget drive where cruise control can be used without feeling guilty. On many new-er cars the manuals are geared much shorter than the autos so for constant cruising an auto might do better considering the lower cruising speed. Certain cars are more simple than others, you'll just have to pop the hood and decide for yourself how much spaghetti you are willing to deal with.

FWIW My brother had an Impala like yours and my fiance has a 2008 with 3.5 V6. My bro isn't an overly aggressive driver and used to get low 30s and I swear my woman's 08 could beat my Focus on my work commute (90% highway) if it were driven the same way.