I have a freshly completely rebuilt Quadrajet 4MV 7040247 on a stock 455ci and it runs good until 60 mph then stalls - as if starved for gas. It also runs good under WOT until third gear, then stalls. Electronic ignition, complete tune up, new electronic fuel pump - 40 gph, fuel line, vacuum lines and oil pressure sending unit on transmission. Vacuum advance on cap is taped off. Could it be another vacuum problem?