Year difference in motor blocks

[Josh521]

I have a 2003 silverado with the 4.8l. Im needing a new motor figured a 5.3 would be easier to find and a better motor. But my question is what other year blocks can i use. Ive heard you can swap the 4.8 for the 5.3 with a tune. But could i fit an 04 - 06 block while keeping all accessories and fuel rails etc. I read in 04 it went to returnless fuel rails. 

[Brian715]

You should be fine. I put an 01 block in my 06. Just kept all the intake and accessories and everything from the 06 except the bottom end. 

[SierraHD17]

Anything gen 3 will interchange physically and will work in your truck. So 1999 to 2007 (classic so the same body as your truck in 2007 only). 

 

You are correct that 04 and newer are return less but just reuse your intake manifold.  The only gen 3s that had different size injectors worth noting were the 99s (smaller) and the L59 5.3 equipped trucks with flex fuel (larger).  4.8 through 6 liter used the same injectors throughout most of the run.