Feeling perkier when it's hot outside isn't necessarily a bad sign. There's a funny physics law with gases, I think it's Boyle's law. My high school physics is a bit rusty. For every 10 degree increase in air temperature, oxygen reduces 3%, or something around there. Engine ECUs have this compensation built in, via the MAF's temp sensor and the exterior temp sensor. So if it's 30 degrees outside (ignoring the actual intake temp sensor for now), you'd expect 9% less fuel being burned (mpg should improve also) compared to 0 degrees ambient, and lean mixtures make more power than rich ones
Mine feels better in summer than it does winter. Sign of a weak fuel pump? Not sure, but the logs always look fine. Weird. It also has a weird dead zone when it's between 10-15 degrees ambient where it feels a bit flat. Odd.
And in the winter months, more fuel is added the colder it gets as the air contains more oxygen.