turbothrush- thanks for the info. I think the VX's "sweet spot" is probably 60mph. Keeping the engine "at/near/below" the 2,000rpm mark "seems" to produce the "best" return (in mpgs).
holycow- I actually looked on the tire the night we spoke about increasing tires pressures, and the tire actually says "maximum psi, 35". these are not the stock tires that came with the vehicle, and they are "slightly" more aggressive tread than what the stock tires would have had. I can't really complain of the results that I get from the yukon, as it get's roughly the 16-18mpg that it's listed to get (it's the 4.8L v8). Plus my girlfriend is much more impatient that I am with driving habbits. She drives the thing like it's a tiny sports car (I don't approve of it, but what are ya' gonna' do?)
Not to mention the fact that I purchased those four tires nearly new (mounted/balanced/installed) for $200 dollars (for the yukon). I figured I would get 30k miles out of them, and than worry about swapping for something else down the road.