Does the fact that you have spread out your industrial zones make pollution more bearable? Anyway i had a similar problem: I had a brilliant city, 75k population, 3 landmarks, loads of decent rewards and well educated and high health system. Then i decided to try a city on my own without the patch (i knew i'd fail anyway ), so i uninstalled everything but the commute patches, the others i kept as i needed the school and clinic patch. Anyway, i went back into the game and decided to see what my 75k city would be like, i forgot that i uninstalled the traffic patch, and i watched my city collapse! Even though i installed the traffic patch again, my city still wouldn't recover.