Ok I just bought an 08 lmm a couple weeks ago and on the hwy my fuel gage barely moves but I was running parts in Conroe a couple of day ago and I only got 209 miles out of one full tank of fuel. With diesel prices climbing I have to figure this out.

 

Typically on the LMM Duramax engines, we see a increase in fuel economy with the DPF removed. Getting 209mi to a tank is definitely on the poor side, look into tuning and an exhaust to allow the truck to perform better and see an increase in economy.