Automotive → When to replace shocks?

How does one determine when to replace shocks on a truck with firm suspension?

With a car, I have used the 'stand on bumper & bounce' to see if shocks arrest the bounce quickly.
Not so easy with my Tacoma.

I know once shocks are shot, tire wear will develop but that seems like a waste and unnecessary wear on suspension & tires.
It is dead give away if there are leaking signs but my experience has it that they tend to wear out before leaking.

Mileage doesn't seem like a very accurate indicator due to variable driving conditions.
Some folks use their trucks almost exclusively on paved roads.
I drive a large percentage on rough dirt roads.

I would sure like to know if there is a way to find the sweet spot where shocks are mostly used up but not to point where abnormal wear is occurring.

There is no easy answer to your question. Shocks today last *much* longer than they did in years past though, I can tell you that. When I started my automotive career, we would replace front shocks on cars at anywhere from 25to35k miles, and every same after. They were cheap then, relatively speaking, and they didn't hold up due to limitations in the design.

Today, with the advent and ongoing development of tight-sealing stainless-steel components and gas charging, they live quite long. You'll see struts going 60-70k plus, and a quality shock such as what you'll find on your Tacoma will typically outlast the struts.

However, plenty of outside influences have an effect, such as ambient temps, road conditions and driving habits. The "bounce" test is still valid too-- If your shocks were tanking, you would notice with that check. Of course external leakage is an instant sign, but generally you will begin to feel that the ride has become harsh, which is not the same as "firm". Harsh just doesn't feel good.

when they fail lol..

as a delivery driver I never touched the frontend of my 05 cobalt and its sittin over 200k miles with original front struts, bushings, balljoints etc. delivering 150 miles a day 6 days a week in a town with notoriously bad roads. car was hard to handle, and the front end felt like its falling off over the smallest road imperfections but it boils down to safety and liability to have your car in tip top shape so its not a contributing factor to determining fault in the event of an accident. I find most vehicles I've owned I would stop letting anyone but me drive em after 100k+ usually on the front struts... sometimes city titties can throw a car around quite a bit when they're as large as the ones out here in west texas