Poor SL-6 Gas Mileage

i am new to the forum but love Dodge Darts, esp SL-6s. Here is my question.

Why am I getting very poor gas mileage? I fill the tank and after short ride, its down to 3/4 full. I am checking the following:

(a) plugs, must ck color today, gap =.030, AUTOLITE 66 plugs
(b) my timing is 5 deg BTDC, 42 deg DWELL
(c) manifold heat control valve is free, must ck if it rotates freely upon rev at idle
(d) carb is HOLLEY 1920 (not the best but adequate)
(e) must ck compression today, rebuild engine at .060 oversize (car was cheap, TX car, no rust, looks like heavy use initially, immediately pulled eng for rebuild and started restoration)
(f) valves set at .010 IN, .020 EX (cold adjustments)
(g) eng has less than 500 miles after rebuild, was fighting hi temps after 15 mins driving, new re-cored rad solved problem
(h) drum brakes not dragging
(i) maybe fuel gauge sender in my gas tank is goofy, anybody know the resistors to ck EMPTY, 1/2 FULL, FULL?
(j) 13 in tires (original size)

What else can I should I be checking? Thx a bunch.