new star washers and some extended dog bones from valley hybrids would be a relatively cheap way to help with your adjustment. Also, check and make sure the little swing arm where the cable splits to either wheel is moving back and forth freely. Adjusting the bell crank stop bolts with the hub off will allow you to see that your getting all of the additional slack out. It seems like if any one little thing isn't working then the parking brake on these trucks is pretty so so.