last month when I went out of town my truck was given me 21.5mpg on the highway and going 70-80mph all the way... and I was also pulling my 5x10 trailer and 4wheeler with 2 big ice chest on the trailer.... I was surprised myself... maybe without the trailer and 4wheeler I could of gotten better... its hard for me to do a good highway mpg checks cause I am always taking the trailer/4wheeler with me when I go out of town...

 

hey guys im back from my trip and i averaged only 15.4 mpg, i drove 325 miles at 61 mph trying to save gas. then i got sick of driving and drove the last 275 at 85-90 and got the same exact gas mileage. so when i was coming home i said screw it and drove 85 halfway until the turnpike and went 90 the rest of the way home, and got 15.4. so thanks for your help

 

narrow tires, belly pan, slow speeds, clean air filter, clean maf, etc. in all honesy, aside from making sure its running right and in tune- the rest will cost you more than they will save on a 1300 mile trip.

 

So true...

 

My 99 rcsb 5.3 Sierra is only getting 14 mpg mixed freeway and city 60 miles freeway 5 days a week maybe 8 miles city it has 3.42's and a drop in K&N filter and Flowmaster muffler. How can I up the mpg?

Also my 01 tahoe is only getting about 15 mpg it has K&N FIPK, 3.73, msd wires, magnaflow duals, 05 e-fans, 180 t-stat, 265-50-20,tornado, tb spacer, w4me tune, and my lady drives it 60-65 miles a day mostly freeway. WTF??? Should it be getting better mileage than this? Any help will be great.....

Thanks
Danny

 

The following is just my opinion, based on some experience, coupled with a little research.

The magic number is 1800 RPM. If you can keep your vehicle cruising between 1800-1900 RPM, you will get optimum mileage (all other factors optimal and constant). This number is the resultant of a gearing/tire size/speed equation.

On top of that, the biggest contributing factors to mileage are:

1) Free-flowing intake
2) Free-flowing exhaust
3) Optimum tune

An optimum tune (tune for mileage) is probably the most critical. My mileage actually went up 2 mpg once I got the Radix. Why? Not because the Radix added mileage, but because the tune for the Radix was so much better than the factory tune. Since the Radix tunes fat (rich) vs. lean, I bet I could get even better mileage if I got custom tuning.

 

umm, not to nit pick (i'm pretty good at taht), but how can a fat tuend s/c be better than stock?

the only real way you gain gas milage is advancing timing or leaning a:f. thats pretty much it.
Im gong to assume its because downshifting because optional for you on the highway

 

I think the timing was pretty conservative from the factory, but a little more aggressive with the Superchips tune from Magnuson, even though it was a little rich.