Classic/Antique Car Repair: fuel pump???, inlet filter, push rod

Question
I have replaced the plugs, wires, fuel filter, air filter, etc... But my 1966 250 IL6 still stutters and stlls at speeds greter than 50 MPH. Runs great otherwise.
Any suggestions?
Thanks, Rick

Answer
The list of "could be's" is a long one. Trash in the fuel tank plugging the inlet filter, bad ignition coil, bad fuel pump, worn fuel pump push rod, carburetor float level low, weak valve springs floating the valves, kink in tail pipe, and more. Now it is a job of testing and inspecting.
Brad