Some none vehicle specific suggestions:
The master cylinder might need to be bled before mounting to the truck, get the air out on the bench, then install and bleed the system normally. I do that with any master cylinder work including hydrovac units, pull the master off it and bleed it on the bench. It is much easier to assure that all the air is removed this way.
The push rod to the master might be too long, it needs to have enough slack that the small feed hole at the bottom of the fluid reservoir is uncovered when you release the pedal, allowing fluid into the actual cylinder and releasing pressure built up in the brake lines. The hole is covered and pressure is built up when the pedal is depressed.
There may be one or two bleeders on the hydrovac, both need to be clear of air.
