Did you try diesel purge yet? That does a good job at unclogging injectors. Otherwise, you will need a 27mm socket and a long breaker bar. I had to literally hang from the bar and bounce with my entire body weight to get mine loose. I'd think that it might be easier with a warm engine.
Did you try an oil filter wrench to remove the fuel filter? I use the strap type wrench that is meant to be driven with a socket wrench. If you have a strong grip, you might also have luck with one of those rubber jar opening pads - great to have in the toolbox.