90 Rancharger brake nightmare

I recently purchased a 90 ramcharger 4x4 with 360 fuel injected engine. I got a steal on it but thats another story. I noticed right away that there was a brake issue. The brakes were real soft so I looked around only to find a horrible rotor on the drivers side front. Decided to change it and also decided to change the front brakes, calipers and the other rotor. This job is not really a big deal to me since I have had to do this on every dodge truck I have had. After completing the job and bleeding the brakes I started the truck and the brakes went right to the floor. Decided to change the master and bleed all four. While bleeding the drivers side rear I found a bad line. Changed that and rebleed all four brakes. While the truck is off the brakes pump up very good and there doesnt seem to be any air in the lines. However as soon as I start the truck the pedal goes straight to the floor.

Do I need to keep bleeding or is there something else I should look at?
Please help.

I could be entirely wrong, but it sounds like there's a problem in the vacuum assist for some reason. Have you taken a look at the fluid levels while the engine is operating?

no, What would that tell me? If I check the fluid while running what am I looking for? I was also starting to think of a vacume problem. Would there be a problem with the power brake booster?

any help?