Is my 340 Overcarbed? Avg 5-6 MPG

OK, now that I have my Duster fresh out of restoration, I am trying to figure out MPG and I am eating gas likes its going out of style! My last two tanks made it 81 miles from full to empty. Not good in my opinion. It is a factory 16 gallon tank. Here are the specs on the motor and the dyno sheets. I am looking at the Air1+2 SCFM column and the avg is 573. I am running a Holley 770 Street Avenger so am I over carbed? Thanks all.

- 340 Small Block Blueprinted and Balanced
- Forged stock crank
- SFI Billet Steel Flywheel
- Centerforce D/F clutch
- Keith Black 0.030 over cast pistons cut to 9.3CR
- Forged rods with ARP Waveloc bolts
- Kevko oil pan
- Melling HV oil pump
- Comp Cams XR286HR-10 Hyd Roller Cam at 105 degree C/L 13 degree @ 050
.544 lift / 286 Duration
- Comp Cams Double Roller Timing Chain
- Comp Cams 8920-16 retro hyd roller lifters
- Comp Cams Double valve springs (140/385 spring pressures)
- Hughes 1502 1.5 ratio roller rocker kit with holddowns
- Hughes custom built pushrods: 5/16" x .083" 4130 HT 7.900"
- Single groove valve stems
- Ported J Heads @ 68cc w/ 2.02" intake and 1.60 exhaust valves
- Edelbrock 7576 Dual Plane air gap intake
- Holley Ultra Street Avenger 770 double Pumper
- MSD Pro Billet Distributor
- MSD Blaster 2 Coil
- MSD 6AL-2 Ignition box

just put your specs in eng dyno and got 409tq @4750 448 hp@6259 , changed the compression to 10.2 and got 446 tq @4750 497 hp @ 6250 . @10.1 441 tq 481 hp

Maybe I made a mistake ? Or maybe the poster was right , to much cam