[GCncsuHD]

Originally Posted by rs74

Would converting over to a 6.0L FI engine make that big a difference in these trucks for mpg's? Not wanting to sidetrack the thread that much but just wondering.

That is the plan for my truck after I am done with my 67 (which is also getting a 5.3). Not so much for a MPG gain, but rather the power and reliability. I had the 6.0 in my 2001 2500HD and loved it, I had 5.13 gears and 38" tires, I routinely got 12-13 mpg (with the 4l80e overdrive), and dropped to about 10mpg towing heavy. Before it was lifted, when it was on 33s with 4.10s I got 16mpg a few times, but normally stayed around 15mpg, and got about 12mpg when towing in the mountains. And that truck weighed probably 1500lbs more than my dually.

Without overdrive, I don't see the 6.0 making a huge increase in mileage, maybe 1-2 mpg, but along with an overdrive transmission you would see better results.

I won't be going overdrive with my swap, as I want to keep my sm465, but the LS engine should be happier cruising along at higher RPMs for long periods of time.