69 C10 disc brake conversion

[Vince69C10]

Hello everyone, i recently did a front and rear big brake disc conversion on my 69. I also converted it to 5 lug at the same time so i bought new rear axles and the kit i bought from cpp came with everything else except for a brake booster which i had from a previous cheaper kit i picked up. My issue is low pressure. My pedal feels soft and i get a loud whining noise from the rear brakes (due to them vibrating back and forth) when i brake at a low speed. When i bleed my brakes the rear shoots out fluid like it shoot, nice strong steady flow. But the front is a smaller flow and doesnt drop the pedal like the rear do. I've tried another new master cylinder, combination valve (using the tool as to not trip the valve), all the fluid and lines are brand new, my booster seems to do its job as it makes the pedal easier to push, I've done the park brake adjustment, bled the master in and out of vehicle, bled the system, tried pinching the lines (made no difference in the feel of the pedal). I am at a loss, has anyone had an issue like this? Any ideas?