98, 5.9, 4x4, 265/75/16 AT tires, 26 gallon tank, 320 miles till its on empty, mixed driving.
I get 220 miles from the fist "half" and about 100 miles out of the last "half" of the tank.
Check your plenum, check valve, and spark plugs. If you have no issues, check your cat, and muffler. I...