4,000 miles ago I did the following to my rig: 4.5 rubicon lift, 4.11 gears, 33 inch tires, detroit true track lockers, air filter, spark plugs and wires, distributor cap, 4 hole bosch fuel injectors, water pump, upgraded alternator, upgraded starter, fuel filter, thicker diff plates, jb conversions super short slip yoke eliminator, tatons shop rear drive shaft, dakota digital box for speedo and throttle body spacer all added/replaced. The re gear was done about 500 miles after the lift (with the lockers of course). I got about 12-13 mpg. After the re gear I got 16-17 mpg, which is about 2 less than what I got stock. I monitor using the torque app and my overhead console. The past 400 miles however I'm back down to 11-12 mpg. Most notably on the highway. 55-65 mph I range 10-11 mpg. At 35-40 mph16-20. Just seems odd that it got that much worse, my travel patterns are the same, even cruise control makes no difference. I was reading around and I dont think my efficiency should be this bad. Typically shifting at 1800 to 2000 rpms. Vehicle equipped with ax 15 trans, Dana reverse 30 front, Chrysler 8.25 rear, 30 gallon skid plated gas tank(had for a few years) heavy duty radiator (5 years), 85k miles on body and engine with the good old 4.0 motor. Tire pressures all good also. Any suggestions on what could be causing this? I like to think I'm thorough, but I must be overlooking something.

 

Bad O2 sensors tanked my mpg once. Use NGK's.

NICE rig by the way.

 

Glad you bought o2 sensors up, had them replaced the other month when a light shot up. Somehow didn't phase mpg too much. Appreciate the feedback.

 

When was the scoop put on the windshield ??

 

Driving habits and fuel brand you use both can cause the lost.