i have a 2004 siverado 2500hd 4x4 it has the stock exhaust that is 2 in 1 out on the muffler i want to add 2 flowmaster mufflers with 2 exhaust tail pipes so that it is true duels i was told that making it true duels it will lose horsepower but that i should pit the flowmaster 2 in 2 out muffler what do you think thanks