It's a truck...that you have heavier tires on and changed the aerodynamics.

This is the "EPA" ratings from my 14 window sticker. I average about 14-15mpg on 87 octane with my truck. It was around the EPA with the stock tires and no lift.

Also look up how EPA gets their ratings...it is a very simple test at speeds much slower than actual speeds. IIRC highway is like 50mph or something like that.

 

I get that but it has never broke 16 on the highway ever... That is my concern more than the city. I have 2005 Duramax, 2020 silverado all same types of mods and this sucks the mostus and has the least amount of get up and feel in power so I am just trying to balance it out is all. I didn't level or put the tires came that way looks great.

Thanks for the input though. Ill tune and plug it and decide. Hell maybe with the tune at least it will be fun getting 14 mpg... LOL

 

Here is EPA rating procedures...average highway speed is 48 mph
The test details tab shows all the tests data in one nice chart. They also do this on a "treadmill" in a building.
https://www.fueleconomy.gov/feg/fe_test_schedules.shtml

 

Levelling and bigger tyres will knock off that MPG.

The bigger tyres are unsprung mass, they're not just killing your rolling resistance (highway MPG) but they're screwing your city driving too, getting those things running, so starting, stopping etc, especially with bigger engines, is what kills their MPG.

 

Well well well.. I got my lazy but out and changed the plugs. I did find something wrong right away, so in one regard that's good plugs weren't needed. The PCV Breather Line was not plugged into the PCV on the driver side. It has been spitting some oil out. The plug was getting oil on it for sure. All my plugs look great, minus this one which had oil on it for sure. I replaced them all anyway and reconnected the house and cleaned the MAF which weren't bad either I have seen worse especially that upper intake one. The truck was not blow your mind difference but the lag and responsiveness felt much much better! Took it for a small drive felt great. Was worth finding that more so than getting new plugs! I am sure it will do little better now.

Regarding tunes. How does the 93 vs 91 work? You have to specifically put 93? I have kind of started looking and all I see around here is 90-91 and that is all I use anyway. Just trying to decide as I am placing my order with MPT today. Thanks for all the input!

 

Whatever tune you run, that is the minimum octane you NEED to use. So 93 tune, must use 93 or higher. 91 tune, must use 91 or higher, 89 tune must use 89 or higher, 87 tune must use 87 or higher octane.

 

Sweet thank you! I was thinking that I just feel ripped off as 91 as good as it get's around here! Thanks for clarification!

I was thinking 91 tow, 91 race and 91 economy? Anyone have thoughts? It does seam like a lot of people run the tow as its not as sensitive as the race?

 

^ I was running just Canned tunes through this month. Just got my custom tunes on Wednesday, drove about 30-50miles so far on the custom
93 PRX MPT tune. I must say it was a huge difference over canned tunes. ( Canned did make a difference over stock though )
But wow, I will never wait again on my next truck for a tune. Appears to be the same mileage compared to Canned tune ( slightly better than stock in city 1-2 miles improved
and 3-4 MPG better on highway (so far) . As long as your not flooring it continuously.
I would suspect 91 would be right up there with 93. My area 93 is readily available.

After about a week or 2 , I will try my other custom 93tow tune just to see. But I am very pleased, feels like a new truck. When you step on it, it will light up the tires easily first and second gear. Just normal driving still more responsive and not annoying

 

I have a couple of questions about tunes on these 3.5's I understand tuning, since I use to own and race Turbo Buicks 87 Grand Nationals, we had to change out the prom that we created on the ECM to make any changes for fuel mapping, boost, timing..etc Back then we certainly made changes to the IC, turbo, injector size, FP sizing..etc the only transmission adjustment that could be made was just converter lock up. Can I assume the stock factory tune is for strictly 87 octane? I ask this because I have seen where others have written about running say 93 octane and they get better performance? Which really shouldnt happen unless the software is always experimenting with timing, fuel curves and boost levels while listening for knock from pre-ignition? So I am confused then why upping octane helps performance.In fact upping octane for a set in stone 87 octane tune might even degrade performance slightly due to its lower volatility? What am I missing here?

 

The simple answer is the software is doing all of those things that you listed. These trucks are computers now and they are looking at everything they can to squeak out the best performance and fuel economy. A tune really just adjusts the set points that the software looks at, that is why it is as easy as just basically uploading a new file to your trucks computer.

The truck also looks at and determines the fuel being used in all of this based on all of the sensor data. It can determine if you are using 87, 89, 91, or 93 and adjust all of the other things accordingly. A tune built for 93 takes that control basically away and tells your truck, you are using 93 or greater so don't even bother thinking you have less than that in you.