2000 ford ranger HELP

can anyone tell me how difficult it would be to replace my 3.0 v6 with a 4.0 v6 I have been told the 4.0 will bolt right up in 3.0s place but would have to replace wiringharness because the original 3.0s harness wouldn't connect to the 4.0 engine is that the case if so how difficult would it be and is there any other changes or any thing i should be aware of before installing the 4.0 in place of the 3.0 that was originally in the truck please let me know your opinions and suggestions on this matter thanks