The common thing I see in similar situations such as this is that many new ssd users have simply cloned and reinstalled the previous setup. I always advise a clean install to get rid of ols settings which may limit your performance such as trialware, bloatware and original manufacturer registry settings that were there for their own system setup.
4k and latency seems a little out of whack.. what's your subsystem? notebook/desktop - intel config, southbridge etc.
if desktop, first try another SATA cable.