we got the 6.0 in a week ago and is doing good! Recap, i have a 1999 ecsb 4x4, originally with a 4.8 that had the leaky castech heads, so i swapped to a 6.0 to avoid getting any more bad heads since they were on 4.8 and 5.3's. This is just our family ride and not a hot rod. Just had a 87/89 octane tune done for the 6.0. It runs great! Just dissapointed with the fuel mileage. The best i could get with the 4.8 was 17.5 on the highway. Freinds with the same truck but with the 5.3 were getting 19 being the bigger engine didnt have to struggle as much, so i figured the 6.0 in a half ton and 4l60e would get at least 18, but it aint looking that way..Looks like its going to be worse than the 4.8...other than that its great!

 

Is it all stock, including the converter? My truck when all stock with the 6.0 got about 17-17.5 on the highway, but its heavy, AWD and 4.10 gears.

 

In stock configuration, the 6.0 shouldn't really get any worse mileage than the 4.8. In fact, I pulled down 23.5 mpg with a 6.0 swap, everything else otherwise stock, 3.42 gears, cruise on 70 IIRC from Indy to St. Louis. 4.10 gears knocked hwy mileage down to 18.

 

ya its all stock, even the convertor. I have 3.73 gears..I figured it would do as good or possibly better than the 4.8..

 

I average 12-14 in mine and it's a factory 2005 LQ9 2WD truck.... Bone Stock

 

I get about 12.5 in town and 17-18 on the highway, truck in sig. From what I have found that is about to be expected......

 

WOW! Thats good mileage..I dont know why mine is being such a pig.. The engine came from a 2004 yukon xl, its an LQ4, all stock and is very clean and runs perfect. I used the original 6.0 injectors that came with the engine and put them in my original intake. Had nelson performance do the tuning for the 6.0, doing an 87/89 octane tune, and had them turn off the rear o2 sensors in case the cats ever go bad and also had them turn off the EGR. No reason why it should use this much gas..

 

It is a 4x4 truck, so thats more weight.

Tire size/ tire pressure and brand can play a roll in lower mpgs too.

Your style of driving too, if you choose 70-75 mph over say 65 mph, you will lose mpgs. How many feet above sea level and if you have many hills affect it aswell.

 

Who did your tuning? Im wondering if nelson got my fuel trims off.. My buddy has a 6.0 he put cam, intake, injectors, throttle body, and headers and had nelson tune it. Then he had it dynoed and it only put down 280 HP, so he had the people who dynoed it tune it and they got 388 out of it! said nelson had the fuel trims off bad..wondering if thats what im dealing with..?

 

You can't know about the fuel trims without scanning it.