My low compression engine died in high gear too, laid over at 5000. Higher compression will make any mopar fly. My 383 had 12.5, 426 Max had 12.5, 499 had 15.4, they all were fast! The 383 ran 7.05 with same heads cam intake and carb as 440 that ran 7.6 with better vert and both had 4.88 gears good slicks, maybe 200 pounds heavier in the 64. The 440 was the only one that wouldn’t rev past 5000, the others went over 7000. Compression!