1996 GMC Savana

My vehicle's engine was reconstructed and now it has a code, cylinder 5 misfire I took it to the mechanic he only changed the connection for it not to have misfires, he then told me if the engine light came back up then he thinks it could be the injector, but did not specify which one. I honestly do not know what to do my van still shaking and I am afraid is going to just turn off and not run.