I am thinking about putting an x pipe on my 1997 vortec 5.7 L . I have true duel ext. with old school glass packs on there now. I don't want to change out any of that. I removed the factory muffler, and installed the 2 glass packs some time ago. Then installed 2 tail pipes, so in front of the glass, there are 2 pipes (factory) and behind the glass packs 2 larger pipes. I also have summit shorty headers on there. The truck has been tuned and has a cold air filter with a 170 degree thermostat. So here is the question, will an X pipe give me more performance? More bottom end? more top end? or just all round better. Common sense tells me top end, but I have never messed with one. And how will effect the gas millage?