So since the repairs, and the fixes of the underbody stuff on my car, I've tried to keep driving habits in check to see what the changes would be. Even with a few (rather needed) WOT freeway entries, and wet road hoonage the last few days thanks to Hurricane Dolly, So far the car has average an estimated 18-20 mpg over the last half-tank!
Compared to the last tank where it barely managed 11 mpg, that's a huge improvement for me!
For the most part, I Neutral coasted off the highways, and engine braked when ever it was good, and other then that a bit slow on the freeway helped a lot. Since I live just off a highway (only way to get anywhere), I figure doing 60-65 instead of 70+ made a big difference.
So, thanks for the bit of help and all the good reading here. Saving my butt some green.

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1990 Pontiac Firebird
3.1L V6, 4 speed auto, 270,000 miles and T-Tops!
Just finished getting it back on the road and in my hands for the 1st time.