I have a 2006 Silverado with a 5.3. The engine is not original..it is from a 2002 Silverado. I swapped all the electrical parts from my old engine and installed it in the truck.. the engine will not start on its own..if I spray starting fluid I can get it to start and eventually idle..but it will not start under it's own power.. also once I put it under load it starts trying to die and wont idle any longer. Does anybody know what could be causing this problem. Any help would be greatly appreciated

 

It would help us immensely if you could do an OBD II scan-tool read-out on your Chevy and post the results here. You might get a scan done for free from an auto parts store,
or spend $35 dollars USD on a low-cost scan-tool to read the codes so we can diagnosis your issue.

 

if starting fluid works, then you have a fuel delivery problem right. The usual procedure applies. Check your fuel pump pressure, then fuel filter, then injectors.