CentralCoaster wrote:
The computer mpg calc assumes a certain fuel pressure and injector flow rate. If your injectors aren't matching this, the computer won't be as accurate.

I think 27 is too high for an 84. 21 is too low for an 85.

Autos will get better city mileage due to the converter unlocking. Manuals usually get better freeway mileage because they're more efficient and let you use engine braking instead of having to hit the brakes as much. But I question the 4+3's efficiency.

My stock '85 4+3 got 24 mpg highway.
Conversion to 6-speed bumped that to 28mpg
Swap from 3.07 to 3.45 dropped it to 25mpg
Cold air intake bumps it up 1-2 mpg in cold weather.