I have a few friends with the 3.0 (Ford and Mazda) and they haul stuff all the time. One buddy hauls feed with his Mazda 3.0. several days a week, plus, he hauls wood, roofing equipment every week for one of his jobs. He got rid of his 2003 4.0 Ranger and got a new 2006 3.0 and already has put over 90,000 on it as a dd. He says that the 3.0 has saved a lot of money on gas bills. 
One of my buddies has a trailer that he takes the lawn equipment out 
everyday for his job. He has put over 130,000 miles on he 2005 3.0 Ranger and he gets good gas milage as well he claims. Now...if he lived in a very hilly area it would not be so good. So, there are good and bad things about the 3.0 to 4.0 motors. Better gas mileage with the 3.0 for one thing.
If you are only thinking about all out performance and don't care about gas milage then stomp on that pedal as much as you want to and get that 4.0.....after all... it will be YOUR TRUCK!!! Get want you want and don't care about what others will say about you. 
$6.00 a gallon gas is coming very soon to a scary gas station near you!!!!