Depending on how serious you are about reducing fuel consumption and how much money you’re willing to throw at it, there are only a couple of things that will really help significanly. Over inflating tires, taping off panel gaps, air filters, exhaust and fuel additives will only do so much.

The main fuel saving techniques:

1. Weight reduction is free, but for significant results you’ll need to pull out hundreds of lbs. 3rd row seats, sound deadening, carpet, spare, etc...

2. Water injection can be used to increase mpg. There really aren’t any plug and play kits I have seen but it would be really interesting to see a write up with cost and before and after data.

3. A low pressure turbo system can theoretically increase mpg if you stay out of the power. I haven’t seen any kits for this either that are bolt on but it certainly would be cool.

4. I would say areo but in town it does nothing and realistically it’s pretty hard to make a brick shaped SUV areodynamic.

Fuel economy is an oxymoron when it comes to the GX

New O2 sensors may restore the original fuel economy. They have an end life even though they have not failed to the point of setting off the engine check light.