can anyone tell me what I should set timing at for a 74 318? TDC or 6 d TDC?

Last month I had to change the distributor in my 318, I dropped it in right at the same point where it was when I removed the old one.
Set the timing at 2 d before tdc and the car was gutless, set it again at like 6 D before TDC and it runs great has great performance but my gas mileage seems to be a lot worse than before.
I drove the car one way 88 miles out to Rio vista to windsurf and it consumed like 3/4 of a tank about 6 3/4 gallons. I thought I was getting about 18 to 22 before I changed out the distributor? not real positive about that but you can almost watch the gauge drop as you drive, not normal.
any help would be great.
The car got the same mileage on the return trip and had to stop to get gas, I know I have driven this before without having to refuel.