My Tahoe will not turn over after engine replacement, any suggestions?

Are you saying it cranks good, but, won't start or the starter motor won't even crank the engine? Is the computer and engine compatible? Battery has a full charge and battery connections all good, not just at the battery, all ends. Positive and negative both are important. in the past, I've seen people forget the engine ground or the chassis ground. Need to check everything. Incase of your security system, I [posted relearn procedure, where applicable.

First double check battery cables to make sure they're clean and tight. If everything looks good, check voltage signal at the stater solenoid. If no signal, trace back to ignition switch. If voltage present but won't turn over, replace startelr.