Another low cost solution to consider is using air shocks.. I've used them for years with relatively little problem..

Even with the extra weight I've added, (rock sliders, rear skid plating, rear dual battery and tool box) the air shocks have provided acceptable lift (I run 95psi in the shocks) to not only overcome the spring sag, but bring the rear height back above original ride height. The shock mounts on the 4Runner are massive and beefy enough to carry weight full time.

I've used both the Gabriels and Monroe air shocks and prefer the Monroes.

The Monroe shock you can use on the 4Runner is the part number MA700..

You may not find it listed for the 4Runner application because the diameter of the lower rubber bushing hole is slightly smaller than what a perfect fit would be.. but, all that means is when you install them, you need to use some WD-40 to lubricate the bushing and a little muscle to get it on the mounting..




Shock installed, fully extended....the bushing in red circle is the one more difficult to install due to the hole being on the small side.


For off roading, the shock allows a bit longer droop of the axle for better articulation, but not enough to have clearance problems..

One caveat..with ANY aftermarket shock.... the metal bushing support rings that comes with some aftermarket shocks are made of thinner metal than the original toyota shocks. I had one of the after market bushings fatigue fail, and allow the upper shock stud mount and nut pull completely through the upper mounting hole.

The upper (most outer ring next to the stud nut shown in the pic below) metal bushing failed, demonstrating that axle rebound shock force (driving on rough surfaces) is considerable, and more of a factor than the compression loading from the shocks carrying weight to support the vehicle.

Save the original Toyota thicker metal bushings and use those on the outer end instead.