Have you verified the booster is working???

Next verify the vacuum that the pump is producing?

is it the only source of vacuum and if not is it plumbed properly?

Do not overlook the pad compound. We have had several kits from different sources that have displayed poor performance. After verifying pressures at the master and calipers swapping in pads with more aggressive compounds did the trick. OF course the suppliers always claimed we were the only ones that had experienced a problem. Sure!!!!