2000 Toyota Landcruiser Gas mileage

As far as the RPM's, that sounds about normal. However, the fuel consumption doesn't. Have you checked everywhere for leaks? Is the air filter clean?

Yes air filter is clean. Brand new along with the oil change that went along with the tune up. When I take my gas cap off it makes a huge sucking sound. I was thinking a vaccume line. I have had many thoughts like egr are the oxy sensor

That is normal for the fuel tank to release pressure when you remove the fuel cap. Has the check engine light ever come on? There are so many sensors that can cause this type of an issue, but without the light, it becomes a guessing game.

Yes my number one coil pack threw the light on so that's y I did the tune up. But after that the light has been off. Would resetting the computer help it cause I do rember they didn't delete that code that made the engine light come on it just went off after a couple days. I don't mean to sound crazy but three quarters of a tank in 120 miles that ain't right

Where should I start on this guessing part

I think I would start by checking the O2 sensors to make sure they are responding properly. You will need a real time scanner.