Help! C20 Disc brake conversion problems.

[Dtech]

So here is the low down, I did a front disc brake conversion on my 1969 C20 and the disc brakes are as bad as the drums were.

I found a 1977 c20 and pulled the spindles, discs, steering linkage
New calipers and brake pads
Used rotors.
Used p valve
New Master for 77
New brake lines for front brakes.
Correct hoses.
New ball joints upper and lower.
Kept original A-arms

Got the swap done. the truck stopped somewhat better, but when I put a ton of brick in it, the stopping power is horrible. When the pedal is pushed hard enough, only the front right tire locks up... barely with the truck empty.

I kept the stock 69 pedal and Brake booster and shaved down the plunger to fit the 77 master cylinder.

Bled the brakes completely.

I'm thinking the brake booster/pedal setup is to blame and not pushing far enough and therefore not building up sufficient power.

If I'm correct, what is my BEST option to handle this. Would I see better results with a 71-22 pedal booster set up. Or is there and ever better option. Ill replace the p-valve new but I don't think this is it. its just something I shoulda done in the first place

I REALLY need help because all this work is for nothing at this point. And the truck is a work truck.

Thanks