[48richard]

I have a 71 longbed, 350/350 with 3.08 rear end and 31.5" tires which are about 10% taller than stock. I kept track of the mileage over 3 years and got 11.5 mpg using it as a driver, about 2500 miles per year.
Then I pulled the engine because it leaked oil. I re-sealed all the covers and intake manifold, painted it and put it back. No more leaks, but over the last 15 months it has averaged only 10 mpg. The only thing that I disturbed that might have some impact is the timing since I removed the distributor, but it is timed properly as far as I can tell, and certainly runs as well as ever.
Any ideas, other than global warming?