340 Gets Terrible Gas Mileage

Hey guys thanks for the quick reply. I will answer some of the questions that I can right now.

I believe the speedometer and odometer is correct.
Not sure what rear gear is in the car. How can I tell what I have?
There is no fuel leak.
Could it be running rich, maybe. After I drive it a bit and come back to start it, I find I need to put pedal to floor while I crank it to start.
Do I keep my foot out of it, mostly but I will gun it from time to time. Guy has to have a little fun right?
I don't know what cam is in it. The place I bought it from did not have that info either.
Rear tires 255/45 R18
Suburban driving cruising 45 mph.
The question about a misfire, it lopes at idle but I believe that to be due to the cam.

Any additional comments would be great because I would like to drive it on a regular basis but 6 mpg might limit this especially if I'm using 93 octane.

Thanks

Dave