I tow my 17z without a WDH with the same truck with no issues. The Tacoma's are known to have soft rear leaf springs and Toyota has a TSB that addresses this issue. Initially when I got my 17z I had some significant sagging and I addressed the problem by installing Firestone air bags. I decided to go with the air bags over the WDH as towing is not the only thing I use my truck for, comes in handy to air up the bags when I got my toys in the bed
. I understand the air bags do nothing to transfer weight to the front wheels but the tongue weight of the 17z isn't much to begin with. Do you have the 3 or 4 leaf spring pack?