Using L9 on the 10 speed transmission

[Alster]

For those using L9 with the 10 speed transmissions, do you notice any difference in fuel mileage ?

 

[sbbobb]

Yeah, my experience shows about 2 mpg less in L9, but mind you it depends on your driving style and roads. My numbers were from the truck's DIC display, not from miles driven and fill-up tracking, so I may not be very accurate. But I like running on all 8 cyls which is my understandind L9 will do.

 

[Stormin08]

this is a loaded question...

what is your tire diameter ? where is most of your driving done ?

mine on a 35" tire saw no loss....but 90% of my driving is on the highway. if you do a lot of town driving on large tires...you would see the gain by using 10th when on the high way

i am curious to see what i do now with the 37, as i already seem to be using lower gears longer...i typically drive it manually

 

[Midnight TB]

There are 3 things to keep in mind when using L9 to keep in V8 mode all the time. 1 it will hold gears longer and not shift as smooth in traffic as just being in normal drive mode. Will be some drivability loss. 2 if you are driving at constant speed above 55 or so, you will be be losing some gas mileage not using that 10th gear. 3 being in V8 mode all the time is also going to hurt gas mileage too.

If you are running stock tires/suspension and drive like a normal human being with a 6.2 10 speed, you will do about 12-14 around town and 18-20 highway. Running in L9 will likely drop you to 10-12 around town and 16-18 highway with bigger declines if you travel above 75 a lot. Not gospel, but a good gauge for you to visualize. Will assume the 5.3 should be very similar.

 

[Stormin08]

my 6.2 on 35's averages about 14.5, seeing 16.5 ish on interstate...in L9 keeping the truck right at or slightly under 2K

i have not done a road trip yet with the 37's, but it i will have numerous to compare to...as most of mine are the same run up and down 55 from STL to LA.

i have never noticed any shifting difference by selecting any gear prior to starting out, the only gear holding i can notice is in Tow/Haul or sport (which i do not have)...but he 24 5.3 truck i run in does.

 

[Stormin08]

odd that all 3 comments regarding downshifts are 24 model years....my 23 does not differ on the down shifts.

i will be paying far more attention to verify, but have been super picky regarding the GM shift schedules since the early 2000's with the 6 speeds.

 

[The Raven]

The results I got did not totally match what I was told (about L9). I was told that driving in L9 disables DFM...and indeed, when I tried it, I noticed a significant increase in responsiveness, the deceleration "shudder" was gone, and it felt a lot more like the old pre-AFM trucks. However my fuel mileage did not change at all. 3 months later I installed the Pulsar LT and disabled DFM that way, and I lost 2mpg. So, I dunno.

I've had the Pulsar for about a year now and along with my 35's and steel bumper/winch setup i've been seeing 15-16mpg in town, 18-19mpg highway. I have the 5.3.

 

[2023 TrailBoss]

What is the pulsar LT?

 

[Keller]

Pulsar is an inline interface with a few programmable features. It only works on 2019 to 2022 pre-refresh trucks though.