First of all, many thanks to everyone who's posted advice and instructions here for swapping out the X-Reas system. I went with Bilsteins and my 4Runner rides better than ever. With that said...
I may have done a dumb thing. I think I may have missed a part when I reassembled the driver's side shock assembly.
The picture for the assembly only shows one shock absorber cushion that goes on top of the Shock Mount/Front Suspension Support Sub-Assembly (Part 48609). However, it also shows a Retainer Washer (Part 48510B) that gets installed under the Shock Mount. The original part diagram calls this a "Front Shock Absorber Cushion Retainer," which makes me think there should be a cushion between it and the Shock Mount. When I installed the new shock, I know I didn't install a cushion between these two parts. Also, I don't recall if the old shock had a cushion when I removed it and sadly I threw it away. On most applications, including the rear shocks, there's a bushing on both sides of the upper shock mount.
What's happening now is that I'm getting a metal on metal slapping/clinking noise whenever I go over washboard road that cycles the suspension quickly. I checked the skid plates, and those are tight. So, I have a feeling it's because I messed up and should have installed a cushion in-between these parts. However, the parts diagram doesn't show one. Does anyone know if there should be a cushion in between the lower washer and the mount; and if so, is the part the same as 48510J, or does the cushion come attached to the underside of the shock mount?