Losing pressure @ Brake cylinder

[Truword1]

Hey list, I purchased a conversion brake kit (drum to disc and power brakes)from ECE. I got everything put together but since Saturday I have been trying to bleed my brakes with no luck. I've bleed brakes many time in my life but I can't seem to get any where with this one. Well here is what is going on. I bench bleed my master brake cylinder but when I put it on the truck I lose pressure. I took the master brake cylinder off and bleed again. Working great but once it goes on the truck it pumps maybe four good squirts of fluid but them I lose the pressure again. I'm thinking that the push rod is either to long or to short not allowing the valves to function properly. Please help, your help would be greatly appreciated.

Thanks
JOhn