Transplant a 5.3
There are a ton of hidden cost with the 5.3 swap that you should know about before you start. Motor mounts and the like are a small part but you will also need a fuel pump that delivers the pressure needed (56-58 lbs) and return to tank line or in-tank pump. Then you will need a harness, modify a stock harness or purchase a new one. Then the ECM and programming. Low end at $800 and up depending on where you get the parts. Total swap as mentioned above at $3K is about right depending on how much you do vs farm out. Do your homework. Later (gen IV) engines have VVT and DoD and 2003 and later are all drive by wire. Don't get discouraged, it's a fun trip.