i have a 1999 silverado v6 with a 2003 5.3, engine harness and harness for under dash but something still isnt right can anyone help out ?

 

you have the wrong color paint for the taillight bulbs on your neighbors car.

 

You don't need to change any harness under the dash that I'm aware of.... Don't know what that is about.

Can you be VERY specific about the problem that you are having. As slogo alludes to-you have not given us enough detail to help you. If we don't understand the question, or what you need help with, how can anyone give you an answer? Tell us what "isn't right" as you say.

 

Remove underhood V6 harness and PCM, install V8 harness and PCM,reflash to remove VATS and other annoying codes, enjoy.

 

The 99 had a egr, 03 did not. Other than that, it should plug and play. Absolutely ZERO info as to "what" isn't right.

 

Another one-post wonder?