Hello everyone, I am new to the forum and new to rebuilding engines so I'm trying to gather some information. I am posting this on several forums to try and get as much input as possible, so if you happen to notice, please don't think of this as spam. So here is the run down:I am doing an engine swap. I originally had a 4.8l 1500 in my 1999 (new body style) Silverado. I purchased a 5.3l 1500 engine from a junkyard that was out of a 1999 Tahoe.

I have had the 5.3L engine rebuilt and would like to install it. I am sure that everything will mount up okay. So to try and keep this short, I want to install a 1999 5.3l 1500 engine, use the wiring harness from a 1999 (new body style) silverado, and use a 2005 5.3l ECM. I've heard some people say yes they will match up just fine (it looks like it will to me, but I haven't actually rebuilt it yet). I've heard others say there will be too many electrical issues. Please provide me with some definitive guidance. Do I need to look into reflashing my 4.8l ECM to run a 5.3l engine?

 

I believe there may be some issues with the programming between the years, I believe the ECM itself will work but needs to be reflashed to the 99 specs.