hmm things you can do, kung under warranty pa yung lens, have it calibrated with your body. ganito ginawa ko sa kit lens ko dati and ganda ng naging result, faster focusing, sharper images.
pwede ding bumili ka ng cheap na flash(nissin di622, sunpak, nikon sb-600, basta pwedeng ma rotate)
mabilis na talaga dapat ang prime pero kung hindi ka pa rin satisfied, sell your 85mm and get a sigma 24-70 hsm or 70-200hsm. ang bilis na nung motor niyan or dagdag ka pa ng konti and get those fast nikkors with vr and motors.