I'd have to agree with pearlkid9988. Going from a 3.0 to a 2.5 is going to be a huge drop. You are already familiar with the performance (?) of your 3.0; the 2.5 is a good engine, but is going to disapoint you even more.
Folks who own the 4 bangers, this is in no way a shot at those engines. great in their own way.
To the OP, these 3.0's were/are used in many Ford vehicles, and are plentiful in the boneyards. You can get them with low mileage, or rebuilt. I have 214K on my original 3.0, and should it give up on me, I plan to keep the truck and dump in another 3.0.