I have 22k miles. For the 18.8 I was running with a/c off, babying it on starts, driving the speed limit, and drafting off other people. I do have a free flowing intake and exhaust along with a tune and 160 t-stat. I run with 35 psi in my tires and use the 93 octane fuel. The 16.7 has been mostly with no a/c, but does include a couple of trips to the track. My truck has really come to life after I added the Flo-Pro HD muffler and had my tune tweaked. I may have stumbled onto a pretty good combination.

 

I am always very skeptical of anyone who has a 6L saying they get better than 18mpg. I baby a 4.8 ebsb and can barely pull 17mpg mixed highway/city

 

Mine gets good MPG. I get about 20 or so when I'm taking it easy. I've got the 4.8L vortec with flowmasters and a throttlebody spacer. Next mods.....hood and cold air intake....

 

Then you should feel like a turd in a punch bowl.6.0 well tuned 1/2ton 18MPH hwy.And awesome torque.the 4.8 is a waste of an OEM order sheet.The 5.3 is fine in a SBRC 2x4.Everything else.......6.0

 

I have 12 grand on my 04 SS I got 19.2 driving from texas to washington st. mods are elec fans, Aem cai, magnaflow exhaust, 160 stat, tb spacer... i dunno if being dropped helps it since it catches less air...

 

Your combo sounds good. I have almost your same mods except, the exhaust system. I have all factory exhaust. Maybe a few more MPG are lost in the exhaust system.

Jim

 

I also have a 4.8 RCSB with a 5 speed, 3.73 rear gear. I have been keeping my foot out of it, but I drive 75mph on the hwy avg. I am getting 17.7 city and hwy combined. I have a 6.0 lq4 and sts turbo set up waiting for me to install. Sounds like I should be getting about the same mph as I am now. Sounds good! Thanks for the info. I think I may have to install a T56 as well for I don't think the nv3500 will hold.

 

Cruising between 60 and 70mph I average 20.8 w/93 octane. Around town, driving like a 3 toed sloth gets about 16.5mpg. The average is SEVERELY skewed my letting the truck idle. With about 50 miles on a tank (and average mpg reset at fillup), I went into the local convenience store and my average mpg dropped from 18.4 to 15.9 during that time!

 

Wow! I didn't think idling would be an issue. I let my truck idle all the time. Good info.

 

i get 9.3 but i drive pretty crazy!