Compu cams XE268H question

I've got the Edelbrock 600 cfm (model 1405) on an Edelbrock Performer, with electronic ignition, MSD 6AL, Comp Cam XE268H, headers, duals.. on my 360.. timing is 35 degrees advanced at about 3000 rpm with Vac Advance disconnected.. I get about 8 mpg
I know it should be getting better than that.. I will be taking it to a dyno/tune shop soon to see what we can do