keep in mind there are 3 types of FJC suspension setups, all the springs are the same the difference is on the shocks.
base: all black Tokico
Off-Road package: silver Bilstein,
TRD: red Bilstein
the reason your Xreas (shocks) fail is "probably" because of the coil springs. just remember, shocks don't lift up your truck, coil springs are the ones which carry the weight and support the frame. shocks being called shocks is because they are there to damp the impact.
Why 4Runner is heavier than FJC but the springs are lighter? 4Runners are designed to feed the needs mainly to the soccer mom's, they want cushy ride and quiet when go through speed bumps. after i swapped out our 4th gen's shocks and coils, i feel it rides better but my wife thinks it's noisier.
this is a side by side pic of 08 FJC OR package front coil over vs. stock 04 SR5, they are the exact same length, but only the FJC coil is made of bigger wire:
take a look at any, i mean any stock 2nd and 3rd gen 4Runner's on the road, they are all sag in the butt. why? because when people buy the new truck, it rode nice and quiet, but over the years when the under weighted springs got tired, they start to getting shorter and shorter.
the best place to find these is on fjc forum. i got my who set for about 120 bucks.
another benefit of switching to FJC is lots of the 4th gen's are still under either standard or extended warranty, all the silver and red Bilstein shocks are labeled as "Toyota", most of the yahoo's at dealers won't know the differece, but if you have after market suspension and take yours in for warranty work, i can guarantee you they will give you some BS about it.