Have you checked your alternator output voltage as you rev the engine? Maybe your voltage regulator is bad and it's producing too much voltage and that's pulling the starter relay in.
'64 Sport Fury, 528 Hemi, FiTech EFI, 4-speed, 4.10 Dana 60 '57 Belvedere 2dr sedan, current project in process '19 Cherokee Trail Hawk Elite '03 Ram 2500 CTD HO, 6-speed 214,000 miles and still going strong
