for your case (over 3 yrs), WOM is very effective way

unless you live in some anti-immigrant district, you definitely shall sue both USCIS and FBI. Recently a few court rule favoriable to plaintiff(I-485 applicant). Particually in Connecticut District, the judge threat that it will grant application GC if USCIS can't adjudicate the case in 30 days (I-485 RD: Aug 2004). you can find lots of information 这里 , also we will post those Judge opinion soon