I have a 1970 429 fresh rebuild was 2 bl motor suposed to be 320 hp 10.to 1 comp in my 89 f 2504x4 .cam is 260 der. 496 lift 750 edl carb no headers offy 360 degree intake cam is advance 4 degrees. I pull a 6000 lb trailer It dont pull like it should can any body give me some advise on why.it is just low on power do i have a bad combo or do i have something else wrong.