Not sure if you guys could help me or not, but here goes.

I just bought an 06 Mercury mountaineer and It came with the class 2 reciver and I want to swap it out with the class 3, any input?

 

Since the hitch is Main part of the bumper assembly, you will be replacing that part. For a visual, the buisness end of the bumber is the hitch assembly with a bumper cover that gives it that regular look. And since you didnt get the upgraded tranny cooler(part of the class 3 towing package) I would suggest a larger trans cooler.