Ive always heard 50,000 miles is when you replace struts, but im sure they can go longer than that. Usually i do the bounce test. Go to each corner of the car and start bouncing the car up and down, then stop and see how long it takes your truck to settle. If it settles to a stop pretty much immediately then you should be fine. If it bounces for a couple more times then it might be time to replace.
The bounce test has never worked for me, perhaps I don't know what I am looking for. It is however reasonably easy to tell when driving - it feels like your bouncing all over everything when their completely shot. I would guess at 117K your probably to that point, but I suppose it does depend on how and where you drive.
I did mine at about 110,000 and they were pretty tired, since they are part of the spring setup it's not as obvious as you think.
One other point is if it's highway miles they have less compression cycles as opposed to local streets. Sometimes a shock can go bad early too.
I posted a thread here back in late 2015 describing my ordeal changing out the original shocks in my 2005. At the time the truck was 10 years old and had about 100k miles. My shocks were trashed. I posted pics of them showing how rotten they were. I had a whale of a time removing them due to rusty bolts. Primarily the lower shock mounting bolt and the three bolts on top of the upper shock mount. I had to cut mine out. At the time I didn't replace the springs, only the shocks which I upgraded to Bilstein 4600s. I also reused the original top mounting bushings which came back to haunt me. I finally replaced them again 2 weeks ago.
To test for spring frequency , you remove the shocks/struts. They have nothing to do with determining spring frequency.
Of course testing is the only way to tune shocks.
My friends run King shocks and have their vehicles tested at the King test track in Barstow.