I have a 92 Silverado 1500 that has the 4.3 v6 and 700r4 trans with 265000 miles. I’m doing a complete frame off restoration. My engine needs a complete rebuild along with the trans. Since I have the truck taken apart I want to upgrade the engine to possibly a 5.7 (NO I DO NOT WANT TO DO AN LS SWAP). I know I need to move the motor mounts and get a different fan shroud and possibly a bigger radiator. Can I use my existing wiring harness and computer on a 5.7? What years will hook to my transmission? Are there any other options I can do? I’m trying to keep this on a lower budget. I didn’t think finding a 5.7 would be that difficult but I’m finding out it is and people are asking good money for engines with 150k or more miles. I would really appreciate any help and suggestions I can get. Thanks in advance.

 

While I cannot address all the questions, I will say that from reading these forums, your existing wiring harness and computer/ECM are for the v6, and won't work with the 5.7. Even switching between say a 5.0 and 5.7 would be problematic I imagine, and at least require an ECM transplant. You will probably need to take the ECM and complete wiring harness from the vehicle the donor 5.7 is coming from.