@ Slowmover
I am not sure why you quoted my post as I don't see what it has to do with your argument but I will say I agree wholeheartedly that fuel is only part of the cost of running a vehicle, though I disagree with the statement about the real money being in tires etc.
Looking at my own personal numbers fuel counts for about 60% of my vehicle costs over the last 4 years (including purchasing the Explorer) Equal priced tires that last 10% longer would save me about $50 a year while burning 10% less fuel would save me about $800 a year.
Of course doing both would save me more and driving less would save me the most.
But we are talking about modding a Suburban and I can't see a problem with trying at least partial wheel skirts in the back. I can't imagine it causing damage to other parts, and I was just trying to keep expectations realistic for what gains to see.
We are all for saving money here, whether through burning less fuel or by other means, it's all good.
