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[Nate66]

Can you build a 2002 5.3 engine and put it into a 2012 Gmc 1500

[silveradosid]

anything is possible you would have to get the ecm and tcm reprogrammed

[SierraHD17]

You could but all you would use is the block.... and the rest is inferior to the newer late gen 3 and gen 4 engines anyway.  The cranks have different amounts of teeth... gen 3 is 24 and gen 4 is 58 so you need a newer crank.  The cam sensor is on the front of the block and not the back plus a 2012 would have VVT which you have no provisions for.  The knock sensors on the 2002 are in the lifter valley and not on the sides like the gen 4.  Plus the gen 4 has better heads ( 243 or 799s), better intake stronger rods, flat top pistons and higher compression and on and on.  

 

So no.... don't even waste your time.