Nice truck. A few tips from another 2wd suburban owner....
Get rid of at least the cross beams for the roof rack. I removed my entire rack and just use a hitch basket in the back when needed.
Go the efan route, it helps on these things.
Get some tuning software and start playing. HP-tuners is really good at logging and tuning. I increased my timing 4 degrees with no knock and can hit 25mpg@80mph in our '99. I know I have more room to bring it up.
Keep the cooling system healthy. Flush and fill should be one of the first things you do. Keep good fluid/filters in the engine and transmission, they like it. A new fuel filter is a must at least once a year. Imagine the junk that 44 gallons of gas constantly getting filtered looks like.
Enjoy the ride. i am sure you noticed that 2wd suburbans are going up in value in some areas of the country. They did follow the prices of 4wd units but, now seem to have switched as buyers become aware of the "not so bad" mileage. It sounds like you did your homework to narrow down what you wanted. Good choice to avoid those toyota vehicles with sludge problems. That's what caused our camry to lose it's engine$$$$$$$$$
BTW: My wife's uncle has a model like yours and hit 21-22 all day long with nothing done to it.