David, all good info has been posted but I'll add my experience.
I went through similar problems getting my stock Hucks setup after a full 100% brake system rebuild.
My pedal was spongy and I'd have to pump the pedal to get a good hard brake pedal.
My problem ended up being that I had several very small leaks.
They didn't leak much but I figure the leaking would suck air back into the system when pressure was relieved which added to the problem.
I had 2 3-way blocks that leaked and one fitting one a rear wheel cylinder. After I found and retightened those joints I've had no further brakeing problems.
How i found them was to have a helper working the brakes while I was under the truck inspecting each and every junction.
Good luck
Dave
