+1.That is a long time, check your state lemon laws. I know in CA you would qualify for a buy back, over 30 days out of service within 18 months is enough.
Does not sound right to me, a new engine due to misfire?? Misfire is almost always fuel or ignition related.
I'd be checking out the lemon laws as well. I really can't believe that they haven't given you a loaner in a case like this. Shame on them.