Increasing tire size is going to negatively impact performance. It in effect makes your gear ratio more mild, hence requires more pedal to get the same output/performance.
Installing an exhaust may cancel out the effect of the tire size increase, but I'd say it's going to be something you'll have to do to see just how much it impacts your truck.

I installed a Magnaflow SIDO on my '05 w/ 4.6L and I immediately noticed better throttle response and an improvement in performance; but, it was the only change I made at that time, so the effects were easy to notice. I can tell you though, the sound is great. I do not find it to be annoying 98 percent of the time and have not noticed any increase in mpg since I'm probably on the gas even more just to hear it.

Getting Exhaust Upgrade
 

Thanks BlackSTX,

That's what I've heard, gonna get the Magnaflow today, still not sure which one, SI/SO or SI/DO. I'll let you know what happens...

New Exhaust Finally
 

Well guys :thumbs up yellow:,

Finally got the Magnaflow SI/SO chrome tip looks/sounds great :happy-dancing:, love it, can't wait to get the Evo Upgrade :cheesy smile: w/custom tunes that will complete my set-up for now...

I kind of thought you'd be happy with the sound, it's not overly intrusive in the cab, yet you hear it when you step on the gas.