^^^^ exactly
I looked into swapping in an LS into my LS with a 4.2 before I bought my SS (which, reminder, is up for sale).
You basically need to find a wiring harness from a V8 truck, the WHOLE harness (engine, dash, and rear) and add it to your truck. The best option for that is same year engine and body, or else you will be changing things like Abs pump, brake lines, rear axle, etc.
You can buy my 2007 for a good price and be good to go. Just saying