I haven't checked the fuel lines but that is a good suggestion. What about fuel filter - should I change that out? Plugs were replaced the day after I bought the car so I cannot benchmark a difference between the old and new but I did use Autolite plantinum plugs which I understand are not the best for this car. I may change them out with some NGK's and see if it makes a difference.

I realize that 100 miles isn't much of a test - I have been keeping a spreadsheet since I bought the car and I plan to do that indefinitely like I did on the 98 GMC k1500 truck that I drove all year last year. In fact that is one reason why I am now driving this car - I averaged 13.45 mpg over the 13,000 miles I put on that truck over of the course of a year! 99% of the time I was in the truck alone hauling absolutely nothing so putting that much gas in it was driving me nuts. For the 4 times a year I needed it to haul my Jeep TJ trail rig it was wasting a ton of money on gas so I decided to get rid of it and just get something different this summer when I need it again. Anyway - keep the good tips coming!

 

I also niticed that sometimes the gas pump clicks off early and then the tank won't get completely full and your math would then be off by quite a bit. You really need to make sure it gets full for accurate fuel calculations. Just food for thought

 

Good point - but I try to go to the exact same pump at the same station whenever possible so I can try to keep track of changes in mpg due to mods and repairs instead of the difference in gas at various stations or pumps, etc.

 

Well because JimBlake brought up the trans issue you can easily check to be sure the pressure lever cable is adjusted correctly;
Drive along light throttle level road at 25 MPH, put the gas to the floor, the trans should down shift to first gear.
Repeat the drive at 27-28 MPH, floor the gas, the trans should downshift only to second gear.
If that pressure lever cable is out of whack it can keep you from getting Torque Converter Lockup at highway speeds.
I'm not sure how big a dent in fuel mileage this test will cause though!! LOL