I have a 2006 z71 the motor blew it had a 5.3 I put a used low mile 4.8 in it. It will turn over but not getting any fire

 

Hi Stumped

You need to double check all your work & make sure all electrical connection's are connected & all are good clean & dry , also you may want to separate them & check for bent terminals therefoer causing a bad connection ,, also most importantly make sure all your grounds are connected & tight. If you have use of a scanner & can check for codes which may steer you in direction and if the you can perform a data stream test while cranking the engine you can see if all sensors are reading and if they are operating within there designed parameters.