I also had this problem with two different KUN25 model vans and it's a known issue at TTTL.
Unfortunately, they are no particular help and were unable to re-adjust back to specification.
When I explained to them that I cannot pass the handbrake test at licensing, because only one wheel locks, I was told by TTTL that that test is archaic and should not be done on the Hilux because it was not designed to function that way and could be damaged in the process.
Solution wise, although I don't have one yet....it's NOT the pads. From my best observations it's a function of a bias which occurs at the cable split under the vehicle.....I love my Hilux, but handbrake design is lacking, considering it can't be adjusted as necessary.
Under the vehicle, the main handbrake cable goes to the split mechanism (under a metal shield, on driver side of vehicle, close to the driveshaft cross).
At/after the split, the cable to left side rear wheel is directly connected with no adjusters along its run. Only the cable running to the right rear wheel has a turnbuckle for cable adjustment.
Weird part is, and you may have to actually see it to appreciate it, no matter how you tighten that right side turnbuckle and adjust at the drum there always seems to be a bias on first engagement to the left (non-adjustable) side.
Even if you tighten the drum roller adjuster on the 'right/lagging' wheel to the point where the wheel nearly locked and then slacken the 'left/gripping side' way loose, when put to he test, the left/slack side grips first. I suspect changing the cable may not help either.
That's my 2cents, hopefully a TTTL tech will weigh in.