About 7 years ago I bought my '99 RCSB. It had a 5.3 from the factory but had 317 heads on it when I bought it. The seller told me he had swapped 317s on in preparation for a turbo but had gotten bored with it. I drove it like this for a few years assuming it was a 5.3. I'm in the process of swapping the cam and installing a set of 706s I had from a 4.8 I have sitting in my shop. I mailed my PCM to BlackBear to tune it and he emailed me back to tell me it had a 6.0 tune from an '02 installed. Before I have him go any further, is there a way to tell, externally, if I do, in fact, have a 6.0 or if it's something else?

Pull the alternator/PS bracket off and on the block it will have numbers cast into it. Either 4.8/5.3 or 6.0

The other way is pop the heads off you planned on popping off anyway and put a tape measure to the bore. 4.0"= 6.0, less = 4.8/5.3

To determine 4.8 or 5.3 if not 6.0, use that same tape measure. If stroke is right about 3 5/8" you have a 5.3, shorter you have a 4.8

That's exactly what I needed. Thank you! I pulled the bracket and confirmed that it does have a 6.0. I'm stoked!

I'm curious about the gas mileage in a short bed 1/2 ton with a 6.0 and headers. Have you ever done the math to check?

Oh, I just saw that you have 20" wheels. Nevermind.

I never checked, before or after the wheels.

MPG really shouldn't be much different at all.

Approximately the same fuel will be burned to make the same power. In other words the same driving requires the same power for equal movement of the vehicle. You need essentially the same amount of air and fuel to do the same work, but a bigger engine is capable of pulling in more air, so you add fuel. But at the same driving as the smaller motor, you'll basically be using the same amount of air and fuel.

With these newer 2014 trucks having 5.3's and 6.2's.. the 6.2's get as good or better MPG than the 5.3 does. The 6.2 has higher compression, which makes for better efficiency.

6.0's get a bad rep on fuel mileage because people often look at TRUCKS that the 6.0 COMES IN and that mileage. That's usually a heavy *** HD truck with a 4L80. But look at a LS2 corvette that knocks down 30 mpg on the highway..