Welcome to the CRG -
Given the working master. I'd say the downstream side is the roadblock. Lest I assume too much, what parts did you use from whom, new calipers and brake cylinders, new or old lines, flush the system before charging ? There are many threads on here concerning rebuilding brake distribution blocks and proportioning valves, which are really suspect in your case. I've heard of failures in new aftermarket and repro parts right out of the box; "new" doesn't always guarantee "works".
I'm sure we can field many theories and suggestions - give us some additional info when you can.
Regards,
Steve