I agree with pgomena - very contrasty situations, I don't see the exposures being far off - the color car show on 8-13 that you feel are most consistent, look like they were shot on a partly cloudy day - less contrast.
I'd sugest trying some shots on a shady day, and other lighting conditions and see what that does.
Also in the Twin cities, I've picked up a couple used lightmeters (Gossen Luna Pro, Minolta 4F) at National Camera and you might find using an incident meter helpful. Whatever method you use I'd suggest staying with one and learning how to get results that work for you.