First, WIth you big tires, your speedo is off unless you have a correct speedo gear.
I bet this is your main problem.
I had 33x9.50x15 tires and the speeod was off 17%.
I had poor power and fair mpg untill i checked and fixed the following problems:
Plugged cat
dirty carb
valve out of adjustment
stuck rings
valve noise (carbon)
carboned up motor
general tune up
HEI dist
desmog (if you can in your area)
When I got my 78fj60, I had a hard time getting over a 1" bump in the concrete at the stop light I stop at every day.
After I solved all of the above, I was driving along and I all of the sudden felt more power. I think the stuck rings and carboned up valves freed up.
I no longer had to slip the clutch to ge over the 1" bump.
I averaged over 15mpg, loaded or empty at any speed (80mph).
Why did you order the parts anyway? Is there a problem you didn't tell us?
