If I were to buy new fx4 shocks for my 02, supercrew 5.4, How much would they be? When should I have replaced them after 02? And how long would they last?

 

....are you serious right now? This type of question isn't why we're here. This is something you can trouble shoot yourself. You don't need us. Google is your friend.

 

Well, there are a ton of shocks out there. Perhaps you should ask which ones people here like the best (it seems to be Biltein 5100 series), look them up and see how much they cost. If you can afford them, ask about the life on them.

They didn't make "fx4 shocks", on the fx4's, they used Rancho shocks.

 

I went with the kyb monomax front and rear on my 01 SC not too impressed with the fronts. I was changing my oil yesterday and looks like one is leaking fluid.

 

Depends on where you get them from.
When they wore out.
Until they wear out.

 

Bilstein 5100's are great

 

More specific..

 

I can't be, there are too many variables to answer that question.

 

It depends on how hot the climate is (remember they are gas charged), how much they get used (do you hit a lot of holes / dips in the road?), how much do you drive? Do you tow? Are your tires in good shape? All this plays into how long your shocks will last.

 

The use of shocks is highly subjective.