95 one ton brake problem

I had a rear line blow so I replaced it and bled the system. But the pedal still went to the floor ! Thinking it must be a worn master cylinder I have just replaced it with a new one and bled the whole system again using my vacuum bleeder. Still no luck, if I pump the pedal a few times I get a LOT of air out of the front right caliper. I have done this about 10 times today with the same result. I have worked on many brake systems over the years but this has got me stumped. With all the bleeders tight there is absolutely no leak anywhere, so I cannot figure out where the air is getting in. I hope someone can guide me in the right direction. Thanks.

If this is an abs equipped truck and the system ran dry, the abs unit must be bled, most times this requires the use of a bi-directional scanner that can actuate the internal solenoids in the abs unit to purge the trapped air.

Thank you for the speedy reply. Yes, this truck is ABS equipped and the system did run dry. However, as it is never used on public roads and I do not have access to a bi-directional scanner, I will have a look at it tomorrow and see if it is possible to remove the brake lines from the ABS module and connect them directly to the master cylinder. Might take a bit of new line and some fittings but should be workable. Thanks again for pointing me in the right direction, I will post the results of my efforts :)