On paper the truck should hit 50mph at ~2750 RPM and 55 at ~3,000 RPM. Your calculations are correct. So the 44mph was "all in" as far as the throttle goes? After the static timing was set, did you ever set the timing while the engine was running? Was the vacuum advance disabled while you set the timing? Was idle speed at the prescribed value for setting the timing? (Reason I'm asking is that is because these distributors start adding in timing advance right at 400 rpm.)
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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