Small Block Stroker ... Gas mileage?

I can get 17+(55-75mph) out of mine,

Hah, I never...

My 408 with a 3000 slippy TCI, through 3.73's and 28" tires gets around 13 highway at 55 mph (2900 rpm's) and 8 city, and that's with a small Edelbrock 650 carb. With the 750 proform DP Holley its 8 mpg highway. However, I can run 87 octane. Edel heads, 236/242 lifting .544/.541, through 1 5/8 and 3" pipes over the axle. Best time thus far is 12.26 @ 109.59 with slicks and the Holley, and 12.73 with a Carter 750 on street tires.

One major Issue I have is the convertor. at 55 mph, it shopuld be revving about 2500 rpm's. but it's closer to 2900. At 67 mph, it should be revving 3000, but it's revving at 3500. I'm not sure how much it should be slipping, but I doubt it is that much!

I was hoping for better mpg, but I don't see it happening without a new convertor, and probably an overdrive.