The 03' 4.0 V6 comes stock 200-210 hp at the crank. Figure about 20-30 % loss through the drive train. 150-160 rwhp. After that I can only direct you to Doug from Bama's Dyno runs. ( Theres a thread he has showing all the charts. They had a 98' 4.0L With intake, headers, 2 1/2 in cat back exhaust, and a excal2 flash he programmed pulling 197 rwhp and 212 ft torque. That 98' also had near or around 80,000 mi. on it if I remember correctly. Thay also did a dyno run on an 02' that had a 3 inch exhaust and a 70mm throttle body and found that it produced only 189 rwhp on it's best run. I think it was running a different chip in it also. Doug was surprised to see that and learned a nice lesson. As for the headers do they do anything, I put them on because if your going through the trouble to put on a cat back, helping to save the motor and flowing that air out better can't hurt can it? even if you only get 2 or 3 more hp, a few little things can add up. As for the sound, I went with Gibson. They are relatively quiet. When I drive normally I can barely tell they are even on the truck. But when I put my foot in it, they truck really grunts nicely! But not much more than if you put a cold air intake on it alone. As to all the warranty questions, intake, and exhaust do not void any warrantees, The flasher is a 5 minute back to stock flash, in to the dealer and when it come home, back to 93 performance flash.
