Make it handle

[cab4word67]

Guys I have leafs in my 67 and lowered 5-1/2" ft and into the C notch tell I almost hit on the rear. My truck will go around 50mph corners at 75mph and the back wont even break loose, street corners the same. What kinda 'G's do you think Im pulling?
Next week we are adding the caster mod and the bump steer mod.
Just a 1-1/4 ft sway bar and viking shocks, oh and cheap tires.