Contour Enthusiasts Group Archives Forums General General interesting fuel economy on my trip, take a guess

so this weekend i went from orange county to stockton(both about sea level) cali which is about 360 miles. recently in mixed city/highway i have been getting around 20mpg which tells me i have some maintainence to do. the trip was mostly flat farm land with one mountain to climb approximately 4000ft in elevation. going north is a 5% grade and going south is a 6% grade. on both downhill runs i did alot of coasting anytime possible to save on fuel. here is the intersting part.

at approx 220 miles we stop for breakfast and i realize there is no way i am going to make it on one tank so i fill up approx 10 gal with 22.5 mpg and i have already both ascended and descended the mountain. not happy.

i get there and do some city driving for maybe 30 of the approx 250 miles and fill up because it is time to head home and my fuel light has just popped on. i get 12.5 gal and 20mpg. really not happy.

i drive 340 point something miles to drop off dad 15 miles from where i live and i fill up on the corner from his place. i get 12.3 gal and 27.69 mpg. really happy, but wtf?

mostly i drove 80mph but my speed flucuated from 65-85mph just depending on traffic. the only difference is going there i used cruise to maintain speed and the gas/brake pedals to adjust my speed. coming home i used cruise to maintain/increase/reduce my speed. beyond that there was nothing done differently and no maintainence performed over the weekend midtrip. the question is: could that one variable really cause a 5mpg difference? the tour has almost 73000 miles and since i only aquired it 3 months ago i do not have specifics concerning prior maintainence.