'09 S, 83K miles, noticeable hesitation under load for first 3 miles from cold, less noticeable once warm. using 91 octane fuel. Bone stock, no mods. No warning lights. Original plugs and coils. Ideas?

 

How long have you had the car? Is this the first time driving it in cold weather? The ECU runs different maps based on cold coolant and ambient temperatures. You should be taking it easy on the car until the engine warms up anyway.