Your PCM will freak out with true duals. Some of the backpressure is required for proper feedback. If you go with true duals be sure you have an x-crossover to fool the PCM into thinking the exhuast is going into a single exhaust. Though you have 2 O2 sensors before and after the cats the PCM expects all the spent gases to mingle at one point and uses the opposite exhuast pulses to draw the gases out.