Hello86,
There are several ways to do this, please find the list as below. I ve tried all 3 modes, all 3 modes will improve the rear ride:
1. Change the rear OEM absorber, brands like rancho, old man emu or bilstein(other brands i m not sure). I m using rancho 9000SL(8 steps soft hard)
2. Replace the rear shackle with a double shackle(tried n tested, this will loosen up much of the tension on rear leaf spring)
3. Replace the rear leaf spring with aftermarket brand - this quite an expensive mod, leaf spring costing of around rm1.8k, your leave this as your last option. I ve opted for for Kings spring, comfort spec - this lower down the carrying load of your hilux(little bit of compromise)
Hope this help