power steering/brake(hydroboost) problem
 

ok everyone i got a power steering problem im getting really frustrated with.

motor is a 93 cummins 12 valve.
i have no power steering at all. i unplug the line that goes from the pump into the high pressure inlet on my hydroboost(in a chevy truck) when the truck is running and nothing comes out with pressure. its like its empty. ive put two brand new pumps on it, nothing. so i pulled a complete ps assembly with vacuum pump off a 91 cummins in my garage that i am 100% sure it worked on. i put it on, and still nothin.

ive pulled the high pressure line, and blown it out, nothing appears to be stuck in there.

i took the front timing cover off to verify that the gear was spinning, and of course it is. but i have no flow anywhere. ive had a total of 4 different pumps on it and 2 different complete units both from working trucks. what am i missing here?

do the dodge pumps maybe not pump enough to flow up hill to hydroboost or what?

anyone got any ideas