i have my truck running great but when im cruising above 3000 and i let out it will back fire thru exhaust about 3-5 sec after i let off gas .if i wack first and second then let off its fine but if i stay in it until third gear then when i let off it will pop hard out ehaust. my timings at 32 and i had it at 35 my plugs look good and are gapped at 32 . my valves are lashed at about 16-18 when hot .ive upped jets and ,lowered jets but still has load bang . it started after first time at track that i can remember . any help would be greatful. thanks for all the help on previous threads.