I would think that anything w/a Cat. & ECU will have O2 sensor... many rigs have (2) O2 sensors.
Zip: I am no expert on this subject, but your dillema sounds like a crank-shaft sensor. Had a problem like once myself...
My Stock 4wd chevy truck (w/a manual trans) gets 10 miles to the gallon... consistenly. It has 33" tires/373 gears & a small lift... 97,000mi always 10 miles to the gallon.