As your topic says "Does more power always mean poor milage"
No not always. My wife drives a 2003 Dodge Durango SLT 4x4, it has three ranges- 2x4, 4x4 high and 4x4 low. It has the 4.7L V8 and a 5 speed automatic transmission, 3.55 rear gears, tow package and power everything.
I drive a 2005 Dodge Durango SLT. Its also has three ranges- "all wheel drive" with 4x4 Lock and 4x4 low lock. Mine has the 5.7L Hemi and a 5 speed automatic transmission, 3.55 rear gears, tow package and power everything.
The 4.7L makes 230 HP and 290 FT. LBS. of Torque.
The 5.7L makes 345 HP and 370 FT. LBS. of Torque.
My 2005 weighs 5200 LBS. I'm not really sure how much the 2003 weighs, but I know its not as heavy as the '05. They get the same milage!, 12 MPG in the city and if I set the cruse at 70 MPH they'll get 19 MPG on the high way.
If I'm pulling our trailer with all our ATV's on it, the '05 gets a lot better milage. It will only down shift one gear on the hills. The '03 will down shift at least two gears (sometimes turning 5000 RPM's) going up the same hill the '05 go's right up with ease. On a flat stretch of highway towing the loaded trailer the '05 will turn 2000-2100 RPM's at 70 MPH. The '03 will turn at least 2600 RPM's at 70 MPH.
If you look at Dodge's window stickers for both, they have the 4.7L getting 14 city / 18 high way and the Hemi getting 13 city / 18 high way. Sometimes more power is better.