Deuce brakes locking up

My problem, I start the truck and without touching the brakes the trucks moves no problem, if I touch the brakes, the brakes come on but won't release. I have adjusted the brakes with the tires off, I have bleed the the system at each wheel and I have bled the air pack. Where do I go next? Is it the air pack? I have 2 extra air packs and an extra master cylinder.. I don't want to start tearing everything apart until I have exhausted evry option. Did I forget to check or do something. I think that I will try rebleeding everything. Is it possible for the airpack to stay open once I have pressed on the brake. Could the air pack need oil as I have read in a post earlier this week? This problem is driving me crazy, the vehicle is my avatar vehicle. It is a Cdn truck but everything is identical to the M35. And for those of you laughing and saying yea it was built by Bombardier they should stick to snowmobiles, somedays I agree with you. All help is greatly appreciated.

Did you change the master cylinder push rod adjustment?? If the petal does not have enough free travel then it can hold the piston in and it will cover the return hole in the master cylinder and fluid cannot return. Also the return hole could be plugged and not letting fluid return. When the brakes lock loosen a bleeder screw anywhere and if it vents fluid then its not returning to the master cylinder. It could be something with the air-pac but usually its the master cylinder.

Thank you for the info, I did back off the brake pedal adjustment, tommorrow I will try the bleeder screw.