My 2004 Chev 4.3 L silverado 1500 will turn over but not crank

"Will turn over but not crank" - what does this mean? Typically, cranking is "turning over". Do you mean the engine cranks but will not start? I don't know the background and source of the "replacement engine" and what came with it when it was installed, so it's absolutely impossible to guess compatibility. Assuming all is installed as designed, it will definitely require diagnostic testing of the fuel, ignition and air intake systems to know what is lacking and what needs to be serviced and repaired. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops

Check the ignition control module