Probably not.....

 

Switched to Wrangler Dura Trac on my 06 LBZ, kept the same size tire as stock just more tread. I seem to have dropped from 17 mpg to 12. Not sure if the two are related, gonna clean MAF and switch from K&N to a paper filter. Can anyone tell me where the fuel filter is? Just got the truck, its my first Duramax, just want to try some easy things before I go to the dealer...

 

fuel filter is against the firewall on the passenger side near the top of the engine bay, tucked under the fuel filter head and intake tubing, remove the tubing and it is much easier to see and get at, you need to be careful with the plastic Water In Fuel sensor on the bottom, and you need to disconnect the wire before removal of the filter, some guys find it easier to do by removing the passenger side wheel well, i can do it from the top, your choice

Good choice on switching from the K&N back to the stock filter, much better filtration and should be able to last 60-80k miles before you need to change it, ive even heard up to 100k miles.. depending on driving conditions

tire change shouldnt have affected mileage, NEVER trust the DIC, its inacurate, always calculate mileage by hand

 

went to AC Delco paper filter, cleaned MAF, switched fuel filter, water in fuel sensor was broken replaced it too. Got up to 14 MPG on my 600 mile road trip tuesday ( hand calc.). the 17 mpg was hand calc. too... Any other Ideas?

 

have you blocked the EGR yet? if not the intake could be nice and full of a tar like soot and oil residue, its very common on these trucks, when i pulled the intake apart to do the head gaskets on mine the tubing, intake manifolds were full of that junk, could be blocking off your intake flow causing a loss of power

Edit: Mine never got good mileage until i tuned it, it was 13-17mpg and its now 18-22mpg, all hand calculated

 

I hear of people in the cold states, the stations switch to a winter blend?? Maybe that would explain the sudden drop?

Have you pulled anything lately? A friend of mine's LBZ, every time he pulls his trailer, it takes a few tanks to get his unloaded milage back to normal.

 

Have one waiting on me when I get back down to MO, gonna start there and then get wider exhaust, hopefully by summer I'll be all tricked out...