I have the same engine/gears but with a 6.5" lift, I went with 35" tires on 18" wheels and I couldn't really notice the power loss driving around town. It's on the highway when you'll go to pass someone that the loss will really be noticeable. As for your MPG loss I can't say because I have a 6.5" lift not the 2.5" level, I did however drop down to 17-19 mpg on the highway from 22-24.
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