Best mpg?

[baxterday]

I just drove from my farm in San Rafael to Buenos Aires, about 600 miles. I got over 18.6 mpg. I was running 5-30 semi-synthetic from YPF and using 97+ octane. I drive about 110 km per hour, about 64, with the air on and about 500 lbs of cargo ie; passengers. I'm very happy with my milage figures as gas, nafta, costs about 67 cents per litre, which is about 2.25 per gallon for the best stuff. I took a 6,000 mile trip around patagonia and averaged over 16 mpg, with many 4x4 miles on dirt roads. Changed oil today to a total synthetic by shell of 5-40, yes I know you're not supposed to run it but I did for many years on another sub. Well, what are your highest mpg figures for real world driving? Oh, I have a 99 k1500 sub, with a 5.7 vortec motor 3.42 rear end w/posi.