Can the 6.6 gas HD hit 20mpg hwy? Got close.

[Jettech1]

On 9/2/2025 at 6:47 AM, EXSlider400 said:

Natchez trace Parkway

I have driven that section several times in MS.  Nice drive but too many Rangers running radar with a low speed limit, I think it was 50 if I'm not mistaken.  Don't speed on that stretch of highway!!  That highway is designed for the top down on a nice sunny Sunday drive in no hurry at all.....lol...Enjoy the beauty but don't use it to get somewhere quickly!

[Chuck FB]

39 minutes ago, Jettech1 said:

Lots of questions here so let me see if I can help you out here.  Let's talk about weight first.  Full tank of gas with me and my wife in it (combined...don't tell her I said this....just kidding...she's a skinny little woman...ok so CAT scale weight is 7800 with just us in the cab).  I have the custom model that came with the 20's on it.  I run them at 65psi not towing, 75 cold when towing to reduce sway.  (Works wonders by the way).  Fuel is the cheapest 87 ethanol I can find, generally Murphy (Walmart) fuel and I have the crew cab.

I don't have the ability like aircraft to monitor tail or headwinds so I have no idea on that question.  Altitude is generally around 1k ft. above sea level.  That changes of course.  Lots of hills and valleys in GA and where we live now in Alabama.  

So to kind of wrap this up a bit, 65mph is the sweet spot for my 22 with the 6 speed.  I generally set the cruise on 72 going back and forth to work these days and it gets mid 15's sometimes low 16's depending on the weather.  If it's cold I always start it up from inside my house to warm it up (I hate getting in a cold vehicle) so that will drop it some as well.

There are a bunch of factors involved when it comes to gas mileage for sure.  I will tell you 93 octane doesn't change a damn thing when it comes to mpg for my truck.  0!!  No change in power, no change in gas mileage, no change other than my account balance...lol....I hope this helped!

 

Dale

 

Your wife will be proud of your explanation or I think so as per her weight, she saves fuel mileage where ever she goes even if she's never realized it !. I wish I would have had a weigh scale completely empty weight of my truck but items were added onto it by circumstance before I was past a weigh scale and I have not weighed it lately as I keep adding more items under the rear seat and in a couple of large totes in the box for tools and tow ropes, a couple of jerry cans of fuel, and the initial steel/rubber comb mud flaps that weigh more than one would think, the bac flip cover, the rubber bed mat and quite a pile of fluid film clinging onto the underside of the truck, that even weighs up !. But anyway factory weight and I am guessing that means with a full tank of gas but I don't know that, it lists it as 7700 lb and there you are at not much more with two people and for sure a full tank of fuel. A High Country with so called leather seats adds weight, and that fifth wheel prep assembly, spray in box liner, and the extra battery and alternator I have up front, and the overload system of a 3500 as that difference to a 2500. Yup I'll have to reweigh it when I have a chance but not with snow/ice clung to it as it looks like that is now upon us. 

 

Around here its 2100 in elevation but various rolling hills to river crossing grades so its not flat as a pancake like some parts further south of the open prairies and I know with my other truck getting onto some highways that are low in elevation and relatively flat sure bump up the fuel mileage. I've driven through Alabama although was the Huntsville area and then south of there down to Panama City and at least in my mind I thought it was relatively flat for the most part but it was over 20 years ago so am sure I forgot some of it. I do know that one day and that would have been early Jan I think and in Huntsville, I saw frost ... I mean brrrr LOL. Yup, if that is anything typical of what winter is like down there, that I could easily deal with, not the hot humid summers though that I imagine you get.  

 

All I use is regular fuel and I suppose I could ask my bulk retailer if he knows what percent of ethanol they put in but I imagine its enough as some years back we didn't have any ethanol in fuel. That was someone else on this forum that talked about premium as well I believe and so it would depend if it was ethanol free for example and the regular had ethanol. They certainly never tuned the engine to respond to premium by the way it seems and GM has never made that claim, Ford though with their super duty 7.3 does make that claim of better mileage if premium is used.  

 

But yes that helps, your not running low tire pressures like I am to enhance the ride at the cost of some fuel and your lighter than I would be with the extra stuff put on the truck and packed in the truck, weight never helps fuel mileage.