I've had multiple occasions where it will tell me 999 miles remaining, I'll drive 20-30 miles and when I restart, I'm down to 500. It's for sure not very accurate, especially when it starts getting down the the final ~ 1 gallon or so.
Welcome.. It it likely related to your tuning. Anytime you're tuning these trucks they are sensitive to changes, so I would start by reaching out to your tuner.
Update..
You can see my fuel logs in my signature, but it seems like I've lost a solid 3 MPG by upsizing to these tires... I would post the obvious answer that I didn't buy a pickup for optimal mileage, but still 22-23 is not bad for a full size truck. I will add, we've had horrible weather...
For me the only other maintenance that makes this different from a gas engine is I replace the fuel filters about every 20k or so.. it's cheap insurance. Your standard air filter/cabin filter is by the book, and oil changes are 5K for me. I run the OEM ACDelco oil in mine I get from Rock Auto...
I agree to that.. but it seems like with ANY modern car now they all have something that impacts them. I've learned to just drive an enjoy what I have.. on my EcoDiesel forum every other post people are talking about failures and how it could impact them with that platform.
Tires were installed today... overall I'm happy. They are pretty quiet. Not stock quite by no means, but a lot better then the Duratrac's I removed.
The pictures really doesn't do it justice, but I was amazed at the stance difference by adding these vs what I had on there.. it really fills up...
I'm using a set of factory TrailBoss takeoffs (Duratracs) and I can't stand the sound anymore. They are the loudest tires I've ever owned and I've owned 35's on a lifted 2500HD Duramax! :D
Anyways, I found this old post from 2 years ago about me complaining then...