True duals, backpressure loss?

i own a 2000 chevy blazer 2 dr. 5 speed manual trans, 4.3 vortec 6 cylinder, and i want to do true duals real bad.....right now i have single in, dual out 2 3/4 inch flowmaster, but i would like to throw in some JBA headers, a couple high flow cats, and two new single in single out flowmaster delta flow mufflers. people keep tellin me not to do it because i'll lose significant amounts of low end torque, which i dont want to do. is this something that WILL happen or is it something that could happen, but no ones quite sure.......and if it WILL happen, how can i fix it to still have true duals, but not have ungodly low amounts of power at start..........please help