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4.8 spun a rod bearing so time for a new engine. Im wanting to go with a 6.0 or at the very least a 5.3, but Im still looking to get halfway decent fuel economy. Truck is a regular cab 2 wheel drive. It already has a built 4l60e, longtube headers and a decent tune. Ill keep the 4l60 trans for sure. By swapping to a 6.0 lq4 or lq9 will I really see a detrimental decrease in fuel economy. I drive mostly highway and dont flog on it except for when I go to the track. Right now its averaging about 17-18 on the highway. I was wanting to do a 6.0 with a mild cam(texas speed 224) and I also have a tbss intake sitting in the garage at the house. Ive searched a lot and found inconclusive evidence. Just want some decent opinions from those who have done it.
 

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youll lose some, maybe 2mpg
 

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Vortec 8.1L Go Fast Parts
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Shouldn't make any difference provided you aren't changing gearing. Maybe 1 mpg lost, but if properly tuned you may see better mileage since you won't have to push the go pedal as hard to keep the truck moving.

To give you an idea, we swapped from a 6.0 (with a 224R) to a 9.0L (547) and went from 16mpg to 15mpg at 65mph.
 

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Really not a big difference between the 5.3 and 6.0 in MPG like they said maybe 2 mpgs.
 
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