Btw, we took our setup above to the CAT scales. Found out we were a lil above or right at some of our limits for towing. Yes, we were only towing between 5-6000 lbs, but there are other weight limits more restrictive for our setup. GAWR, GCWR, GVWR, Hitch Weight, etc.
IIRC, The max combination weight of vehicle and trailer is 12k on the V8 with WDH.
If you're towing heavy loads, be sure to use WDH and put a fair amount of weight in the back of the 4Runner to keep it steady.
Here's an important tip: Be sure to MATCH the size and type of tires on all 4 wheels of your 4Runner! I was running 6 ply LTs all around and decided to try 10 ply LTs on the rear first.
What a mistake! Although this has never been an issue on any other vehicle I've owned (as long as you matched overall size and had matched set on each axle), the XREAS freaks out when the flex/bulge/compress/whatever ratios don't match between opposite diagonal tires (front drivers to pass rear, etc). It felt like I was riding on a set of broken leaf springs :jaw:
For those who haven't had that pleasure, I'll try to describe it. The body sort of floats around and on corners as the body starts to lean into the corner, it feels like the body is tight, then 'slips' and the edge you're leaning against moves- sometimes inward, sometimes outwards. Sort of like you would feel if your tire slipped on mud or ice while cornering, then grabs again unpredictably.
I was ready to toss the 10 ply, but instead put 10's on the front, too, after several months. I didn't drive it much for a few months for other reasons

I was also thinking maybe the suspension was bad, stuff like that.
AFter putting (a brand I like better) 10s on the front, too, she got rock steady again :rockon:
The lesson here is 1) IF you are going to tow regularly or heavy, upgrade to LT tires. 6 or 10s is fine. I run one vertical inch over (online calculators to figure it for other sizes) 265/70 R17; and 2) Ignore your previous experience telling you it is okay to put heavier grade tires on the rears alone. Although it helps for towing (good), the XREAS compromises the handling (bad), so be sure to go all 4 when you do make the switch.
I definitely recommend a sway control bar, too. The one like I use can be had at etrailer com for about $40 and mounts with or without WDH. I tow a number of different things, but not all with WDH/sway control. Light loads properly dispersed tow quite steadily without.
I have been quite pleasantly surprised at this 'little engine that could' when towing

I say that because when I tow the boat (Crownline 225CR), my 4Runner really does look like a matchbox car! Surprisingly, it hauls better than the camper, due to the aerodynamics, which the camper lacks.
Hope this is helpful.