'84 K10 getting 8.9mpg....is this normal?

[tucsonjwt]

Drive like grandma on her way to church on Sunday - very slow when accelerating from a stop, let off the gas way before you come to a stoplight.
One quick/rough way to check your speedometer accuracy is to note your odometer reading as you pass a mile marker on the freeway - drive to the next mile marker - did your odometer turn over exactly one mile?
The most accurate way I found to check mpg is to pull off the freeway and fill up to pump shutoff. Go directly back on the freeway and set the cruise at the speed limit. Drive about 10 miles, then turn around and go back to the same gas station. Return to the same pump and let the pump shutoff the same way. Divide miles traveled by gallons used and you have accurate highway mpg. The last time I did this I got 13 mpg, which I think is accurate for my 83 big block 4:10 axle, with gear vendor OD.