I get about 14.5-15 city, and 17.5-18 highway with my 5.3 and 3.73s.

 

i have a 00"rcsb stepside.
5.3l w/4.10 gears. 28" tires
just took a trip about a month ago. All most all highway it got.........
22mpg---this is an average speed of about 85mph.

 

I Have A 03 ECSB 5.3 3.73 gear, I get 14-16 city and 20-22.5 on the road at 70-75 MPH.I found that when I use the cruise control it logs better mpg.

 

no, you just drive like a *****

 

 

yeah 80 at 2k is good, but remember these are aerodynamic bricks. When I had an 18 mile highway commute with my 4.8 I hit 21 only a few times, with it being more like 17-19 the other times (can't keep your foot out of it all the time right).

 

i wouldn't doubt that the cause for your poor mileage could be from the short 17 mile drive to your work. your truck sees its worse mileage when warming up and making many short trips, maybe 20 trips per tank minimum, really hurts your mileage. the good part is that your job is only 17 miles away, i'd rather get bad mpg on a short drive than good mpg on a long one. but thats just my take

 

Stock I got good mileage, ext. cab 3.73's 2wd city=15-17 hwy=19-23. A lot of it depends on your driving style of course, but I'm either a full throttle or no throttle kind of driver haha. I will honestly say that the K&N helped my mileage by at least 1 mpg over stock. It was noticed only on highway mileage though.

Besides the mileage stuff, I wonder how much more aerodynamic our trucks are than that 87 s/b? It can't be too much could it?

btw what year and model did the 5.3/4L60E come out of?

 

i have 3.42s with mods below, driving 85-95 and playing at some stoplights i was getting 17.8mpg, best i have seen, driving sensible, just over 21mpg

 

Try driving 70mph or less even with the 3.08's it will help the most and take advange of the gears. At 80 the drag is alot more than 65 or 70 and puts more of a load just like if you were towing a trailer.

So if you trying to save money drop the speed and you should see 20mpg.