Random Burb questions

[HarrisonTX]

Hey guys.
Im thinking of getting my first suburban, and im pretty excited.
I just have a few random questions
I like the 1990 models which i think range from 1987-1991? am i correct on that?
Is it true that they get awful gas milage?
I have a '69 3/4 truck, and i drove from fort hood, to fort worth, every single weekend for almost a year, gettin 10mpg. I spent almost exactly $400 a month, and that was before i went to iraq, now gas is even more, im scared to return to the states.

Since they come with a much welcomed overdrive 4 gear, is that going to help tons?

There alot of 3/4's floating around, aside from maybe a different rearend ratio, does the fact its a 3/4 effect mpg?

I could see me definently installing some 3.08's to help on the freeway, along with a k&N system.

What about 4x4, if its not engaged, does the 4x4 stuff effect milage much?

What are some common problems with theres years?
Anything to look out for?

Just to put it out there, i want a black one, with dark tent, and some black wheels.

These are so cheap on ebay, i dont think there was one over 5k, and alot of them had one owner. Awesome.

Thanks in advance guys.