Why iPhone 4S lag

Normal gta 3 didn't lag on a iPhone 4S which is 7tines faster than a iPhone 4 but why my iPhone 4S ios7 running gta 3 have some lag pls can some one help me I just restore my phone last time on iOS 5 it didn't lag now what's the problem is it the phone or the app bug?? Or the iOS??
Asked Oct 12, 2013

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