340 cam change

I ran a mopar 280 474 cam and changed to the lunati 703 and gained nothing. Then I went to a Hughes solid 237 242 @50 537 542 lift and gained 2.5 tenths. Car was a 68 dart 3550lbs. 9.6 comp. Rpm, 750, headers, 3.55s and 2400 stall. Ran 13.2 and 12.90s with the Hughes cam.