Help with advice on what older Suburban to buy-differences??

[OverRunWithSons]

We have a 1988 Chevy Suburban that is rusting out profusely, and needs an entire back window & tailgate. (Husband installed 3rd seat when we bought this one used). We are soon to be a family of 8. I think our Suburban is a 1/2 ton (I am the wife by the way, so I do not know much), not a 3/4 ton. (this has an effect on Gas milage, right??), we don't plan to pull anything heavy, just kids & take vacations with this thing. God help us with Gas prices!! We are most interested in getting something that can fit 8 of us with the BEST gas milage possible. Our '88 has a Standard shift that we will miss, and we replaced the Power windows with Winders -which we will also miss, why it is that all vehicles today have power everything? then when you go to buy used, it is all JUNK & nothing but a Nuinsance. Anyway, what do you all suggest when looking for the best gas milage (Which motor should we be looking for, which to stay away from??) , we are only willing to pay up to $6,000 total for an older Suburban, Yukon, etc --any other suggestions, it also must be 4x4 because of country living & steep driveway. Should we look for something that has "Overdrive" , does this save on gas milage? generally, how long do these Auto transmissions last -when buying used, I dont want it to break down right after I buy. All advice greatly appreciated. Do people sell on here also? We live in Western PA, 50 miles from Pittsburgh, not too far from Ohio line. I know what we are looking for , we will basically never find, but would choose .....1/2 ton, winder windows, a Standard would be a plus and 3 seats, barn doors in back if possible (these are usually lower maintanice, right?) Thanks !