Hydraulic clutch brake not working.

With the two clutch brake deal you are making up for wear on other components. Then the new problem is they are to thick. The gap must be adjusted to 5/8's- 3/4" to start with and then install the second brake. Then the clutch free play must be adjusted to about an inch. That is just preliminary and it is fly by the seat of your pants. You do not want the clutch fork pushing on the throughout bearing or it will have a short life. Then when you mash the clutch it will hit the brake fairly high off the floor. The amount of travel between brake and clutch engaugement is pretty small so adjustments require tinkering for best results. Use the thinnest brakes you can find and grind the friction material off between the disc's before installation, PPD's recommended. Then adjustment must be checked regularly because of the close tolerances. Never saw a hydraulic in a truck like yours but air in the system can do the same thing. Some of them are very hard to bled out. Sometimes pieces of broken springs can be found it the bottom of the flywheel housing and you know to waste no time on it. Bad master and or slave cylinder can also do that. Sorry no easy answer, it is kind of an experiance judgement call thing that I cannot expain 100%, good luck