Depending on what you have and your desired destination for the truck will determine
if you need a 4-in or more exhaust. If you have a very mild chip and a intake, then
just removing the muffler will do the job. The muffler internals are only 3-inch pipe, so
just putting in a straight pipe or a straight through muffler can get around 80-85% of
the job done. If you plan on going all out, then you might as well get the 4-inch now.
I know the 4-inch really helped mine, but didnt try just removing the muffler. It was
like adding another chip.