I think the consensus around here is that anywhere from 60k to 100k miles is an appropriate time to replace the shocks and struts.
I did it when I was swapping to my H&R's around 75k ish and looking at the shocks they were not in the best condition.
The FX is not like a standard car or anything of that nature because it is big heavy and has a pretty sporty suspension layout and setup. Therefore you can expect to do shocks as a maintenance item, not an item you replace when it breaks.
After 80K on your original shocks, when you replace them now I guarantee you will feel a difference in the ride...