I am thinking about putting duals on my truck. I know that it has a cat. but i am thinking about cutting it off. If i do this, what is the dimensions of the pipe there? 3" or 4" and what size would be best to go with for the rest of the way, 3 or 4. and how long of piping do i need. If i put like a 5" tip on it, how much of a difference will it make. If u dont know the correct length, how far down the bed should i go and will i have any complications like with the spare or the hitch??