There really won't be a power different. Instead, you can just use the power your (assuming 3.0) puts out in different ways.
I prefer the feel and control of a manual transmission. I like to know that the only options my truck has for giving up is spin tires or kill the engine. I also like to just be able to roll over things without having to get into the throttle as much. Depending on tire size, a manual may give you more drive-ability on the highway as you get to be in control of gear ratios.
An auto on the other hand is easier to drive. You may lose a little bit of power to the wheels due to TC slippage, but it is much easier to drive. You don't have to worry about the engine dying as much because the TC acts as a cushion between the engine and the rest of the drive-train. You just have to throttle the engine to build the pressure to get the auto up and over things. You'll have less control on the highway.
I'd take the manual any day, but many will disagree.
