Is it easier to swap a 5.7 ltr or a 4.7 ltr into a 2008 dakota with a 3.7 ltr v6

The v6 doesn't have enough power or torque

You are probably making a mistake to do the engine swap unless you swap the tranny too. The tranny for your 3.7 is not designed for the load of a 5.7, or even a 4.7, even though it will bolt up fine. The next thing is that the computer will probably need to be changed out because it is designed for the 3.7. Then, of course, the exhaust, radiator, and other things should be swapped too. Why not just trade or buy another Dakota that comes with a V8?