I have a 99 Z71 EXT cab with a 5.3 and a 3in body lift. What would I need to do to swap it for 6.6 duramax.

 

Considering the 6.6 Duramax is not a 1999 engine, you will likely be swapping out a LOT of stuff under the hood, including the ECM, getting it reprogrammed, the entire engine wiring harness. Gonna be a bit of work.

That said, if you have a 5.3, that was not a 1999 engine offering either, so has someone already done an engine and computer swap in this vehicle? 1500 came with 5.0 or 5.7, 2500/3500 had 5.7, 6.5 diesel or 7.4...

 

with that said that is a lot. And no the engine wasn’t swapped. That is the factory engine from my truck. 5.3 vortec. Pretty much everything in my truck is factory under the hood.

 

Ok, I screwed up. I was on Rockauto.com looking at 1999, and chose "C1500", instead of "Silverado 1500". Apparently in 1999 they were still selling the C/K that one last year, so I had looked at that instead of further down the list at Silverado. Stock engines for the 1999 Silverado included a 4.3L V6, 4.8L V8 and 5.3L V8. That's it though. The Silverado 2500 offered a 5.3L and 6.0L V8 (gas, not diesel).

The real issue is gonna be the computer (ECM) and wiring harness. To swap to the Duramax diesel engine is going to require help from someone who really knows what they are doing, and probably needs an ability to reprogram or swap out the ECM and integrate the new engine wiring harness with the vehicle wiring harness.

 

The best shop to do a swap and to build a motor for anyone is in Griffin Georgia!
Jeff Garmon in Griffin, GA. Garmon's Diesel Performance. Hands down the best diesel mechanic in the state.404-557-4972
I don’t know the guy but I know a lot of people that have been there and everyone says he’s the best to do anything you want done !
Farm trucks to full on race trucks !