91 305 GMC 1500 Timing Issues

I recently has to replace my engine after breaking a crank an I am now having timing issues with the new engine. I unplug the wire have it timed at zero as it says and sounds great and still sounds good after I plug the wire back in but on take off and when I lift it hessitas and every now and then will shut off. I rechecked the timing still dead on at zero. Would it be ok to run with out the wire hooked up or what suggest would anybody have.