Cycle issues?

[Persistant]

I have been waiting for my new system to finish cycling since the prawn went in November 27. It still has nitrates in the range of 25. Here's the system and what I have done so far.
90 gallon Display drilled with 2 1.5" drains, 1 1" return, 33 gallon sump, bubble trap, live rock in sump, Vertex 250 skimmer. Display has live sand (about 3" Carib Sea Fiji), about 180-200 lbs of live rock. Live rock was bought from an established 200 gallon system, went into a food safe garbage can with heater, powerhead, saltwater to cook. Was cooking from June to November when it went into the display. During the cooking I did check nitrates for something to do and found about the same levels right up to going into the display. Now I didn't check ammonia or nitrites during the last 2 months but the LFS store did. At 9 weeks to try to get it to finish off we did a 50 gallon water change and threw in a 500ml bottle of Cycle. Week later nitrates are still the same….
Am I just impatient or is there something I should or shouldn't have done?