what am i doing wrong?

hey guys i need your sugestions, my 1970 dart 340 swinger with my *** in it weighed 3500 lbs on e-town scale at nats. my motor was dyno'd @ 425hp w-35 degree of timeing @6300 rpms. has 3" exhaust. 727 trans rebuilt to stock with 3200 stall converter, and shift kit. i have frame connectors, an 8.75 rear with hvy dty posi unit, 3:91 gears , and mosler axles, caltrac traction bars , and 15" rubber all around. bf goodrich drag radials on rear. also qa-1's in all corners.when i first got her back from shop i put 300 miles on her before going too track. i now have about 600 miles on drive train. 1st time out i stood at tree with revs just high enough too keep plugs clean , about 1000rpm. my shift points were 5400 rpm, best time was 14.832.
at e-town nats first 2 runs tires were @ 15lbs of air and launched at 1000 rpm. best time was 14.333. last run of day i went down too 12 lbs of air and threw a borrowed spare tire in trunk, lef at 1200rpm, launched good and hard.(see 1st photo link in general boards"onehellofadart pics at e-town).ran 13.83. shift points were 5600 rpm, motor pulled smooth all the way down, with nose up.
what am i doing wrong, motor man says i should be doing low 12's. will going too 1500 rpm launch, and shift point of 5800 bring me there? any suggestions will be appriciated, except weight cracks.

tony