Hi bigsp,
There are a few ways to evaluate the condition of your shocks/struts. One way is a visual inspection. Any oil leakage or grease stains near the 'shaft seal' is a good indication that they're due to be changed. Another way is what's known as a Jounce test. This is when you rock the truck up and down vigorously then let go on the "down-stroke". After letting go, the truck should continue one full travel upwards, then find it's 'equilibrium' at curb height... It should never continue to bounce beyond this point!
The other thing is tire wear pattern. If the tires are 'scalloped'; choppy looking treads, it's telling you that the tires are 'skipping or bouncing' and spending way too much time off of the ground, which makes it nearly impossible to "stop... on a dime", a very dangerous condition! Just know that the 'X-REAS' suspension system is very expensive and usually replaced 'as a system' e.g., hydro-lines, center absorber, 4 shocks, etc! As a result, many here have opted to replace this system w/a more conventional shock... so choose wisely, Best to you!
rigtec, cheers