I have a cracked "53" block in my 2000 3500 and want to know if a 5.9 Cummins "55" from a 2000 2500 will work for me. I cant imagine that they would be different but better to ask now than to find out once I have a motor that will not work. Thanks!

 

I have no reason to believe the same year engine will not be a drop in.
Pre 2000 had a crank sensor near starter that has worn plenty out. Make sure you know what you.re purchasing. do you plan on doing some maintaince inspections prior to exchange. Are you comfortable with history of engine, like see the truck it came from. This would give ideal of type of use.
Most make mistake of trying to upgrade to later year or find a older engine and try to make fit. Good for you.