My old truck went 13.65 on stock Allison with a transgo jr, 4" exhaust, EFI, and suspension work. I was cutting 1.72-1.80 60' times with 285/55 nitto's on 20x8.5 wheels with +10 offset.
Suspension wise on my old truck. I had a straight centerlink, sleeves, new idler arm, new pitman arm, DJM...