This page is to help those guys out with swapping a 1996-2000 Vortec 4.3L to a Vortec 5.7L.  If you do this correctly its not that difficult to do.  2001-2003 is a little more involved as the Computer systems changed for those models.  GM used that newer computer in the 2002 Chevy Express 5.7L vortec vans and so the programming is available.  I just don’t have the wiring diagrams handy for that swap.  Swapping engine mounts and such is pretty straight forward.  its the wiring that gets most people.  My recommendation is to keep the 4.3L computer system which we can flash with the correct V8 programming ($200) and then just alter the wiring for the injectors.   One of my customers sent me these wiring diagrams for his swap in a 2000 S10 Blazer.  Notice that we are not just adding 2 wires for the extra 2 cylinders.  Vortec computer systems are sequential injected so we have to worry about firing order as well.  You will need to move some wires for the 6 current injectors and then add the 2 wires.  Now note that these wires are just for the grounds of those injectors, They still need power. You could just hook those extra 2 injector wires to a key on power source but really you can just connect them to one of the other power wires for the other 6 injectors as GM only runs 2 fuses for all the injectors so they mate them all up at the fuse block anyway.  You will need to get the V8 injector plug that plugs into the top of that intake for those injectors as I don’t think GM used the same plug for both V6 and V8 with just empty holes for those injectors.  If I am wrong let me know.  This minimal wiring change will make your V8 swap in your S10 or fullsize go much easier.   These wiring diagrams should work just fine for the 1998-2000 swaps but the 1996-97 could be a little different. These wiring diagrams came from Alldata.  If any of you do a 96 or 97 swap and find out whether those wires are in different locations on those, if you send me a copy of the wiring diagrams I will be glad to post for everyone to use.